Custom derivative method in ODE solver.

l_r_mcglashan · November 25, 2010, 09:02

Hello,

When using the ODE solvers, I want to calculate the derivatives. This is reasonably complicated so I have a separate class for doing this.

The problem is that the derivative method in the ODE base class is 'const'. So I can't do the following:

Code:

  void
    MyODE::derivatives
    (
        const scalar x,
        const scalarField& y,
        scalarField& dydx
    ) const
    {

        myDerivativeCalculator.solve();
      
        for (int i=0;i<nEqns();++i){
            dydx[i] = myDerivativeCalculator.getSources(i);
            myDerivativeCalculator.setY(y[i]);
        }

    }

...unless I declare myDerivativeCalculator as mutable in the header of MyODE.

I was wondering why the derivative method is const, and the best way to get around this.

balkrishna · January 28, 2011, 00:12

In a similar situation ,I wanted to calculate the numerical jacobian in one of my cases . Have you found a workaround for this ? Besides this is OpenFOAM a good platform to solve a system of differential algebraic equation system ? As of now , I am using SUNDIALS ......

November 25, 2010, 09:02	Custom derivative method in ODE solver.	#1
l_r_mcglashan Senior Member Laurence R. McGlashan Join Date: Mar 2009 Posts: 370 Rep Power: 23	Hello, When using the ODE solvers, I want to calculate the derivatives. This is reasonably complicated so I have a separate class for doing this. The problem is that the derivative method in the ODE base class is 'const'. So I can't do the following: Code: void MyODE::derivatives ( const scalar x, const scalarField& y, scalarField& dydx ) const { myDerivativeCalculator.solve(); for (int i=0;i<nEqns();++i){ dydx[i] = myDerivativeCalculator.getSources(i); myDerivativeCalculator.setY(y[i]); } } ...unless I declare myDerivativeCalculator as mutable in the header of MyODE. I was wondering why the derivative method is const, and the best way to get around this. __________________ Laurence R. McGlashan :: Website

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January 28, 2011, 00:12		#2
balkrishna Senior Member Balkrishna Patankar Join Date: Mar 2009 Location: Pune Posts: 123 Rep Power: 17	In a similar situation ,I wanted to calculate the numerical jacobian in one of my cases . Have you found a workaround for this ? Besides this is OpenFOAM a good platform to solve a system of differential algebraic equation system ? As of now , I am using SUNDIALS ......