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| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="math_toolkit.policy.pol_tutorial.user_def_err_pol"></a><a class="link" href="user_def_err_pol.html" title="Calling User Defined Error Handlers"> |
| Calling User Defined Error Handlers</a> |
| </h4></div></div></div> |
| <p> |
| </p> |
| <p> |
| Suppose we want our own user-defined error handlers rather than the any |
| of the default ones supplied by the library to be used. If we set the |
| policy for a specific type of error to <code class="computeroutput"><span class="identifier">user_error</span></code> |
| then the library will call a user-supplied error handler. These are forward |
| declared, but not defined in boost/math/policies/error_handling.hpp like |
| this: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">policies</span><span class="special">{</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_domain_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_pole_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_overflow_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_underflow_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_denorm_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_evaluation_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_indeterminate_result_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| |
| <span class="special">}}}</span> <span class="comment">// namespaces |
| </span></pre> |
| <p> |
| </p> |
| <p> |
| So out first job is to include the header we want to use, and then provide |
| definitions for our user-defined error handlers that we want to use. |
| We only provide our special domain and pole error handlers; other errors |
| like overflow and underflow use the default. |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| |
| <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span> |
| <span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">policies</span> |
| <span class="special">{</span> |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_domain_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span> <span class="comment">// Ignoring function, message and val for this example, perhaps unhelpfully. |
| </span> <span class="identifier">cerr</span> <span class="special"><<</span> <span class="string">"Domain Error!"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">();</span> |
| <span class="special">}</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_pole_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span> <span class="comment">// Ignoring function, message and val for this example, perhaps unhelpfully. |
| </span> <span class="identifier">cerr</span> <span class="special"><<</span> <span class="string">"Pole Error!"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">();</span> |
| <span class="special">}</span> |
| <span class="special">}</span> <span class="comment">// namespace policies |
| </span><span class="special">}}</span> <span class="comment">// namespace boost{ namespace math</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Now we'll need to define a suitable policy that will call these handlers, |
| and define some forwarding functions that make use of the policy: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span><span class="special">{</span> |
| |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">;</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span> |
| <span class="identifier">domain_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">>,</span> |
| <span class="identifier">pole_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">></span> |
| <span class="special">></span> <span class="identifier">user_error_policy</span><span class="special">;</span> |
| |
| <span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">user_error_policy</span><span class="special">)</span> |
| |
| <span class="special">}</span> <span class="comment">// close unnamed namespace</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| We now have a set of forwarding functions defined in an unnamed namespace |
| that all look something like this: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">RealType</span><span class="special">></span> |
| <span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tools</span><span class="special">::</span><span class="identifier">promote_args</span><span class="special"><</span><span class="identifier">RT</span><span class="special">>::</span><span class="identifier">type</span> |
| <span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">RT</span> <span class="identifier">z</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span> <span class="identifier">user_error_policy</span><span class="special">());</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| So that when we call <code class="computeroutput"><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">)</span></code> we really end up calling <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span> <span class="identifier">user_error_policy</span><span class="special">())</span></code>, |
| and any errors will get directed to our own error handlers. |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of erf_inv(-10) is: "</span> |
| <span class="special"><<</span> <span class="identifier">erf_inv</span><span class="special">(-</span><span class="number">10</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(-10) is: "</span> |
| <span class="special"><<</span> <span class="identifier">tgamma</span><span class="special">(-</span><span class="number">10</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Which outputs: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting">Domain Error! |
| Pole Error! |
| Result of erf_inv(-10) is: 1.#QNAN |
| Result of tgamma(-10) is: 1.#QNAN |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| The previous example was all well and good, but the custom error handlers |
| didn't really do much of any use. In this example we'll implement all |
| the custom handlers and show how the information provided to them can |
| be used to generate nice formatted error messages. |
| </p> |
| <p> |
| </p> |
| <p> |
| Each error handler has the general form: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_</span><span class="emphasis"><em>error_type</em></span><span class="special">(</span> |
| <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> |
| <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> |
| <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">);</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| and accepts three arguments: |
| </p> |
| <p> |
| </p> |
| <div class="variablelist"> |
| <p class="title"><b></b></p> |
| <dl> |
| <dt><span class="term">const char* function</span></dt> |
| <dd><p> |
| The name of the function that raised the error, this string contains |
| one or more %1% format specifiers that should be replaced by the |
| name of real type T, like float or double. |
| </p></dd> |
| <dt><span class="term">const char* message</span></dt> |
| <dd><p> |
| A message associated with the error, normally this contains a %1% |
| format specifier that should be replaced with the value of <span class="emphasis"><em>value</em></span>: |
| however note that overflow and underflow messages do not contain |
| this %1% specifier (since the value of <span class="emphasis"><em>value</em></span> |
| is immaterial in these cases). |
| </p></dd> |
| <dt><span class="term">const T& value</span></dt> |
| <dd><p> |
| The value that caused the error: either an argument to the function |
| if this is a domain or pole error, the tentative result if this |
| is a denorm or evaluation error, or zero or infinity for underflow |
| or overflow errors. |
| </p></dd> |
| </dl> |
| </div> |
| <p> |
| </p> |
| <p> |
| As before we'll include the headers we need first: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">math</span><span class="special">/</span><span class="identifier">special_functions</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Next we'll implement our own error handlers for each type of error, starting |
| with domain errors: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">math</span><span class="special">{</span> |
| <span class="keyword">namespace</span> <span class="identifier">policies</span> |
| <span class="special">{</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_domain_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| We'll begin with a bit of defensive programming in case function or message |
| are empty: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">if</span><span class="special">(</span><span class="identifier">function</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">function</span> <span class="special">=</span> <span class="string">"Unknown function with arguments of type %1%"</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">message</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">message</span> <span class="special">=</span> <span class="string">"Cause unknown with bad argument %1%"</span><span class="special">;</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Next we'll format the name of the function with the name of type T, perhaps |
| double: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">msg</span><span class="special">(</span><span class="string">"Error in function "</span><span class="special">);</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">function</span><span class="special">)</span> <span class="special">%</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">).</span><span class="identifier">name</span><span class="special">()).</span><span class="identifier">str</span><span class="special">();</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Then likewise format the error message with the value of parameter <span class="emphasis"><em>val</em></span>, |
| making sure we output all the potentially significant digits of <span class="emphasis"><em>val</em></span>: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">msg</span> <span class="special">+=</span> <span class="string">": \n"</span><span class="special">;</span> |
| <span class="keyword">int</span> <span class="identifier">prec</span> <span class="special">=</span> <span class="number">2</span> <span class="special">+</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">digits</span> <span class="special">*</span> <span class="number">30103UL</span><span class="special">)</span> <span class="special">/</span> <span class="number">100000UL</span><span class="special">;</span> |
| <span class="comment">// int prec = std::numeric_limits<T>::max_digits10; // For C++0X Standard Library |
| </span><span class="identifier">msg</span> <span class="special">+=</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">message</span><span class="special">)</span> <span class="special">%</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">io</span><span class="special">::</span><span class="identifier">group</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">setprecision</span><span class="special">(</span><span class="identifier">prec</span><span class="special">),</span> <span class="identifier">val</span><span class="special">)).</span><span class="identifier">str</span><span class="special">();</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Now we just have to do something with the message, we could throw an |
| exception, but for the purposes of this example we'll just dump the message |
| to std::cerr: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">msg</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Finally the only sensible value we can return from a domain error is |
| a NaN: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">();</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Pole errors are essentially a special case of domain errors, so in this |
| example we'll just return the result of a domain error: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_pole_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">user_domain_error</span><span class="special">(</span><span class="identifier">function</span><span class="special">,</span> <span class="identifier">message</span><span class="special">,</span> <span class="identifier">val</span><span class="special">);</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Overflow errors are very similar to domain errors, except that there's |
| no %1% format specifier in the <span class="emphasis"><em>message</em></span> parameter: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_overflow_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">function</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">function</span> <span class="special">=</span> <span class="string">"Unknown function with arguments of type %1%"</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">message</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">message</span> <span class="special">=</span> <span class="string">"Result of function is too large to represent"</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">msg</span><span class="special">(</span><span class="string">"Error in function "</span><span class="special">);</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">function</span><span class="special">)</span> <span class="special">%</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">).</span><span class="identifier">name</span><span class="special">()).</span><span class="identifier">str</span><span class="special">();</span> |
| |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="string">": \n"</span><span class="special">;</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="identifier">message</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">msg</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| |
| <span class="comment">// Value passed to the function is an infinity, just return it: |
| </span> <span class="keyword">return</span> <span class="identifier">val</span><span class="special">;</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Underflow errors are much the same as overflow: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_underflow_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">function</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">function</span> <span class="special">=</span> <span class="string">"Unknown function with arguments of type %1%"</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">message</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">message</span> <span class="special">=</span> <span class="string">"Result of function is too small to represent"</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">msg</span><span class="special">(</span><span class="string">"Error in function "</span><span class="special">);</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">function</span><span class="special">)</span> <span class="special">%</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">).</span><span class="identifier">name</span><span class="special">()).</span><span class="identifier">str</span><span class="special">();</span> |
| |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="string">": \n"</span><span class="special">;</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="identifier">message</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">msg</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| |
| <span class="comment">// Value passed to the function is zero, just return it: |
| </span> <span class="keyword">return</span> <span class="identifier">val</span><span class="special">;</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Denormalised results are much the same as underflow: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_denorm_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">function</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">function</span> <span class="special">=</span> <span class="string">"Unknown function with arguments of type %1%"</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">message</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">message</span> <span class="special">=</span> <span class="string">"Result of function is denormalised"</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">msg</span><span class="special">(</span><span class="string">"Error in function "</span><span class="special">);</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">function</span><span class="special">)</span> <span class="special">%</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">).</span><span class="identifier">name</span><span class="special">()).</span><span class="identifier">str</span><span class="special">();</span> |
| |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="string">": \n"</span><span class="special">;</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="identifier">message</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">msg</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| |
| <span class="comment">// Value passed to the function is denormalised, just return it: |
| </span> <span class="keyword">return</span> <span class="identifier">val</span><span class="special">;</span> |
| <span class="special">}</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Which leaves us with evaluation errors: these occur when an internal |
| error occurs that prevents the function being fully evaluated. The parameter |
| <span class="emphasis"><em>val</em></span> contains the closest approximation to the result |
| found so far: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> |
| <span class="identifier">T</span> <span class="identifier">user_evaluation_error</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">function</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">message</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">val</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">function</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">function</span> <span class="special">=</span> <span class="string">"Unknown function with arguments of type %1%"</span><span class="special">;</span> |
| <span class="keyword">if</span><span class="special">(</span><span class="identifier">message</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span> |
| <span class="identifier">message</span> <span class="special">=</span> <span class="string">"An internal evaluation error occurred with "</span> |
| <span class="string">"the best value calculated so far of %1%"</span><span class="special">;</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">msg</span><span class="special">(</span><span class="string">"Error in function "</span><span class="special">);</span> |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">function</span><span class="special">)</span> <span class="special">%</span> <span class="keyword">typeid</span><span class="special">(</span><span class="identifier">T</span><span class="special">).</span><span class="identifier">name</span><span class="special">()).</span><span class="identifier">str</span><span class="special">();</span> |
| |
| <span class="identifier">msg</span> <span class="special">+=</span> <span class="string">": \n"</span><span class="special">;</span> |
| <span class="keyword">int</span> <span class="identifier">prec</span> <span class="special">=</span> <span class="number">2</span> <span class="special">+</span> <span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">digits</span> <span class="special">*</span> <span class="number">30103UL</span><span class="special">)</span> <span class="special">/</span> <span class="number">100000UL</span><span class="special">;</span> |
| <span class="comment">// int prec = std::numeric_limits<T>::max_digits10; // For C++0X Standard Library |
| </span> <span class="identifier">msg</span> <span class="special">+=</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">format</span><span class="special">(</span><span class="identifier">message</span><span class="special">)</span> <span class="special">%</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">io</span><span class="special">::</span><span class="identifier">group</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">setprecision</span><span class="special">(</span><span class="identifier">prec</span><span class="special">),</span> <span class="identifier">val</span><span class="special">)).</span><span class="identifier">str</span><span class="special">();</span> |
| |
| <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">msg</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> |
| |
| <span class="comment">// What do we return here? This is generally a fatal error, that should never occur, |
| </span> <span class="comment">// so we just return a NaN for the purposes of the example: |
| </span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">numeric_limits</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">quiet_NaN</span><span class="special">();</span> |
| <span class="special">}</span> |
| |
| <span class="special">}</span> <span class="comment">// policies |
| </span><span class="special">}}</span> <span class="comment">// boost::math</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Now we'll need to define a suitable policy that will call these handlers, |
| and define some forwarding functions that make use of the policy: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> |
| <span class="special">{</span> <span class="comment">// unnamed. |
| </span> |
| <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">;</span> |
| |
| <span class="keyword">typedef</span> <span class="identifier">policy</span><span class="special"><</span> |
| <span class="identifier">domain_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">>,</span> |
| <span class="identifier">pole_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">>,</span> |
| <span class="identifier">overflow_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">>,</span> |
| <span class="identifier">underflow_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">>,</span> |
| <span class="identifier">denorm_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">>,</span> |
| <span class="identifier">evaluation_error</span><span class="special"><</span><span class="identifier">user_error</span><span class="special">></span> |
| <span class="special">></span> <span class="identifier">user_error_policy</span><span class="special">;</span> |
| |
| <span class="identifier">BOOST_MATH_DECLARE_SPECIAL_FUNCTIONS</span><span class="special">(</span><span class="identifier">user_error_policy</span><span class="special">)</span> |
| |
| <span class="special">}</span> <span class="comment">// unnamed namespace</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| We now have a set of forwarding functions, defined in an unnamed namespace, |
| that all look something like this: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">RealType</span><span class="special">></span> |
| <span class="keyword">inline</span> <span class="keyword">typename</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tools</span><span class="special">::</span><span class="identifier">promote_args</span><span class="special"><</span><span class="identifier">RT</span><span class="special">>::</span><span class="identifier">type</span> |
| <span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">RT</span> <span class="identifier">z</span><span class="special">)</span> |
| <span class="special">{</span> |
| <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span> <span class="identifier">user_error_policy</span><span class="special">());</span> |
| <span class="special">}</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| So that when we call <code class="computeroutput"><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">)</span></code> we really end up calling <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">tgamma</span><span class="special">(</span><span class="identifier">z</span><span class="special">,</span> <span class="identifier">user_error_policy</span><span class="special">())</span></code>, |
| and any errors will get directed to our own error handlers: |
| </p> |
| <p> |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span> |
| <span class="special">{</span> |
| <span class="comment">// Raise a domain error: |
| </span> <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of erf_inv(-10) is: "</span> |
| <span class="special"><<</span> <span class="identifier">erf_inv</span><span class="special">(-</span><span class="number">10</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="comment">// Raise a pole error: |
| </span> <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(-10) is: "</span> |
| <span class="special"><<</span> <span class="identifier">tgamma</span><span class="special">(-</span><span class="number">10</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="comment">// Raise an overflow error: |
| </span> <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(3000) is: "</span> |
| <span class="special"><<</span> <span class="identifier">tgamma</span><span class="special">(</span><span class="number">3000</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="comment">// Raise an underflow error: |
| </span> <span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Result of tgamma(-190.5) is: "</span> |
| <span class="special"><<</span> <span class="identifier">tgamma</span><span class="special">(-</span><span class="number">190.5</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span> |
| <span class="comment">// Unfortunately we can't predicably raise a denormalised |
| </span> <span class="comment">// result, nor can we raise an evaluation error in this example |
| </span> <span class="comment">// since these should never really occur! |
| </span><span class="special">}</span> <span class="comment">// int main()</span></pre> |
| <p> |
| </p> |
| <p> |
| </p> |
| <p> |
| Which outputs: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting">Error in function boost::math::erf_inv<double>(double, double): |
| Argument outside range [-1, 1] in inverse erf function (got p=-10). |
| Result of erf_inv(-10) is: 1.#QNAN |
| |
| Error in function boost::math::tgamma<long double>(long double): |
| Evaluation of tgamma at a negative integer -10. |
| Result of tgamma(-10) is: 1.#QNAN |
| |
| Error in function boost::math::tgamma<long double>(long double): |
| Result of tgamma is too large to represent. |
| Error in function boost::math::tgamma<double>(double): |
| Result of function is too large to represent |
| Result of tgamma(3000) is: 1.#INF |
| |
| Error in function boost::math::tgamma<long double>(long double): |
| Result of tgamma is too large to represent. |
| Error in function boost::math::tgamma<long double>(long double): |
| Result of tgamma is too small to represent. |
| Result of tgamma(-190.5) is: 0 |
| </pre> |
| <p> |
| </p> |
| <p> |
| Notice how some of the calls result in an error handler being called |
| more than once, or for more than one handler to be called: this is an |
| artefact of the fact that many functions are implemented in terms of |
| one or more sub-routines each of which may have it's own error handling. |
| For example <code class="computeroutput"><span class="identifier">tgamma</span><span class="special">(-</span><span class="number">190.5</span><span class="special">)</span></code> |
| is implemented in terms of <code class="computeroutput"><span class="identifier">tgamma</span><span class="special">(</span><span class="number">190.5</span><span class="special">)</span></code> - which overflows - the reflection formula |
| for <code class="computeroutput"><span class="identifier">tgamma</span></code> then notices |
| that it is dividing by infinity and so underflows. |
| </p> |
| <p> |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2006 , 2007, 2008, 2009, 2010 John Maddock, Paul A. Bristow, |
| Hubert Holin, Xiaogang Zhang, Bruno Lalande, Johan Råde, Gautam Sewani and |
| Thijs van den Berg<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
| </tr></table> |
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