| [/============================================================================ |
| Boost.odeint |
| |
| Copyright 2011-2012 Karsten Ahnert |
| Copyright 2011-2012 Mario Mulansky |
| |
| Use, modification and distribution is subject to the Boost Software License, |
| Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at |
| http://www.boost.org/LICENSE_1_0.txt) |
| =============================================================================/] |
| |
| [table Adaptive step size algorithms |
| [ [Stepper] [Tolerance formula] [Norm] [Step size adaption] ] |
| [ [`controlled_runge_kutta`] |
| [ |
| ['val = || | err[subl i] | / ( __epsilon[subl abs] + __epsilon[subl rel] * ( a[subl x] | x[subl i] | + a[subl dxdt] | | dxdt[subl i] | )|| ] |
| ] |
| [['||x|| = max( x[subl i] )]] |
| [ |
| ['val > 1 : dt[subl new] = dt[subl current] max( 0.9 pow( val , -1 / ( O[subl E] - 1 ) ) , 0.2 )] |
| |
| ['val < 0.5 : dt[subl new] = dt[subl current] min( 0.9 pow( val , -1 / O[subl S] ) , 5 )] |
| |
| ['else : dt[subl new] = dt[subl current]] |
| ] ] |
| [ [`rosenbrock4_controller`] |
| [ |
| ['val = || err[subl i] / ( __epsilon[subl abs] + __epsilon[subl rel] max( | x[subl i] | , | xold[subl i] | ) ) || ] |
| ] |
| [['||x||=(__Sigma[subl i] x[subl i][super 2])[super 1/2]]] |
| [ |
| ['fac = max( 1 / 6 , min( 5 , pow( val , 1 / 4 ) / 0.9 ) ] |
| |
| ['fac2 = max( 1 / 6 , min( 5 , dt[subl old] / dt[subl current] pow( val[super 2] / val[subl old] , 1 / 4 ) / 0.9 ) ] |
| |
| ['val > 1 : dt[subl new] = dt[subl current] / fac ] |
| |
| ['val < 1 : dt[subl new] = dt[subl current] / max( fac , fac2 ) ] |
| ] |
| ] |
| [ [bulirsch_stoer] [['tol=1/2]] [-] [['dt[subl new] = dt[subl old][super 1/a]]] ] |
| ] |
| |
| [/ |
| |
| safe = 0.9 , fac1 = 5.0 , fac2 = 1.0 / 6.0 |
| |
| value_type fac_pred = ( m_dt_old / dt ) * pow( err * err / m_err_old , 0.25 ) / safe; |
| fac_pred = std::max( fac2 , std::min( fac1 , fac_pred ) ); |
| fac = std::max( fac , fac_pred ); |
| dt_new = dt / fac; |
| |
| |
| fac = max( fac2 , min( fac1 , pow( err , 0.25 ) / safe ) ) |
| ] |