MATLAB: Problem with too many inputs into bvp5c

bvp4cbvp5c

Hello, I want to test whether bvp4c, bvp5c and bvp6c solvers produce the same solution. The problem I face is that bvp4c and bvp6c allow my ode and bc functions to have additional inputs. Namely, these solvers have the following syntax: function sol = bvp4c(ode, bc, solinit, options, varargin) function sol = bvp6c(ode, bc, solinit, options, varargin) The solver bvp5c however, does not allow for varargin: function sol = bvp5c(ode, bc, solinit, options)

So, does anyone know how to go about this issue? Is there a way to manually edit bvp5c to allow for additional inputs?

Thanks, Artem.

Best Answer

You should not use additional inputs at all, even some integrators still support this ancient method. See http://www.mathworks.com/matlabcentral/answers/1971: Use anonymous functions to provide parameters. This is explained in the documentation also: https://www.mathworks.com/help/matlab/ref/bvp5c.html:

 Parameterizing Functions explains how to provide additional 
 parameters to the function odefun, ...

with a link to: https://www.mathworks.com/help/matlab/math/parameterizing-functions.html.

Related Solutions

MATLAB: I’m trying to solve a fourth order ordinary differential equation using the bvp4c function. However, I am getting a few errors in the code.

function main
  options = bvpset('stats','off', 'RelTol', 1e-6);
  solinit = bvpinit(linspace(0,1,500),[1,0,0,0,0,0]);
  sol = bvp4c (@OdeBVP, @OdeBC, solinit, options);  
  plot (sol.x, sol.y(1,:));
end
% Define ODE
function f = OdeBVP(x,y)
  f=[y(2);y(3);y(4);5*(y(1)*y(4)+4*y(5)*y(6));y(6);-5*(y(2)*y(5)-y(1)*y(6))];
end
% Define Boundary conditions
function res = OdeBC (ya,yb)
  res = [ya(5)-0.5;yb(5)-1.0;ya(1);ya(2);yb(1);yb(2)]
end

MATLAB: Initial guess for bvp4c

There are three parts to this problem:

1. Error: Too many input arguments.

To solve this issue, the second argument to bvpinit should have 2 entries instead of 3. This is an initial guess for all the mesh points. The fsode function accepts the y input argument which is expected to be a 2-length vector in your case. You can read more about 'yinit' argument here: https://www.mathworks.com/help/matlab/ref/bvpinit.html#mw_1c665a1d-6f2b-438a-95eb-6c6a2cd19026

solinit = bvpinit(linspace(0,infinity,2),[25 0]);

2. Even with this change you will see an error that the defined constants are not available inside the functions.

To do that, you will have to pass them as inputs to your fsode and fsbc functions. Some examples are available here: https://www.mathworks.com/matlabcentral/answers/274406-ode45-extra-parameters#comment_351560. Some sample code is given below which you can adapt from:

sol = bvp4c(@(x,y) fsode(x,y,rsco,rje,rd,beta_,pac,pev,fi_), ...
    @(y0,y1) fsbc(y0,y1,rsco,rje,rd,beta_,pac,pev,fi_),...
    solinit);
function dfdeta = fsode(x,y,rsco,rje,rd,beta_,pac,pev,fi_) %Function 
 dfdeta = [y(2)
        (4/beta_)*((y(1))^(1/4)-1)];
end
function res = fsbc(y0,y1,rsco,rje,rd,beta_,pac,pev,fi_) %Boundaries Conditions
res = [y0(1)
      -((4*fi_)/beta_)*(y1(1)^(1/4)-1+pac-pev)];
end

3. With these changes, the script would compile but might throw warnings.

If you see the warning: Unable to meet the tolerance without using more than 5000 mesh points...

You could experiment with appropriate initial choices and boundary conditions. You can also refer to the answer here for some ideas.

Here are a couple of examples from the Docs which should help you better understand how the bvp4c and the bvpinit functions can be used:

a. Solve Second-Order BVP

b. Using bvpinit for an initial guess of BVP solution

Best Answer

Related Solutions

MATLAB: I’m trying to solve a fourth order ordinary differential equation using the bvp4c function. However, I am getting a few errors in the code.

MATLAB: Initial guess for bvp4c

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