Solve a system of 3, 2nd order boundary value problems using bvp4c

Hello, I want to solve a system of 3 boundary value equations. All three of them are 2nd order. Now I have created my dydx by converting them into 6 ODE's. Since they are huge equations (almost 30 lines) I can give you a gist of them. Baiscally its

eqn1:  d2y1/dx +dy1/dx+dy2/dx+dy3/dx+y1+y2+y3+x = const1 
eqn2:  d2y2/dx +dy1/dx+dy2/dx+dy3/dx+y1+y2+y3+x = const2 
eqn3:  d2y3/dx +dy1/dx+dy2/dx+dy3/dx+y1+y2+y3+x = const3

Now to put the above equations into bvp4c I converted the above 3 set of equations into 6 set of equations in 1st order ODE's

eqn1: y(2)
eqn2: y(2)+y(4)+y(6)+y(1)+y(3)+ y(5) = const1
eqn3: y(4)
eqn4: y(2)+y(4)+y(6)+y(1)+y(3)+ y(5) = const2
eqn5: y(5)
eqn6: y(2)+y(4)+y(6)+y(1)+y(3)+ y(5) = const3

I know the boundary values of the original 3 equations. They are:

y1(0) = 0.6; 
y1(20) = 0; 
y2(0) = 0.3; 
y2(20) = 0; 
y3(0) = 0.005; 
y3(20) = 0;

I have written the bcfun function like this:

function res = bcfun(ya, yb)
res = [ya(1); yb(1); ya(2); yb(2); ya(3); yb(3)];
end

And I have written the bvp4c code like this

      ya(1) = 101325*0.6;
      yb(1) = 0;
      ya(2) = 101325*0.3;
      yb(2) = 0;
      ya(3) = 101325*50e-06;
      yb(3) = 0;  

solinit = bvpinit(linspace(0,4,5),[1 0], linspace(0,4,5),[1 0], linspace(0,4,5),[1 0]);

sol = bvp4c(@myodesubfunc, @bcfun, solinit);

xint = linspace(1e-20, 20e-6, 50)
yint = deval(sol, xint)

After running this I get an error

??? Error using ==> myodesubfunc
Too many input arguments.

Error in ==> bvparguments at 106
    testODE = ode(x1,y1,odeExtras{:});

Error in ==> bvp4c at 130
[n,npar,nregions,atol,rtol,Nmax,xyVectorized,printstats] = ...

Error in ==> bvp at 28
sol = bvp4c(@myodesubfunc, @bcfun, solinit);

If you can help me with the syntax ( just a small part of it) that will great

Thanks, Nitin Nair

Answer 1

[Walter Roberson]

Since it is the myodesubfunc function that is being complained about, we need to see the code for myodesubfunc .

Answer 2

[Nitin]

For myodesubfunc I wrote the code like this

function dydx = myodesubfunc(x,y)
dydx = [ the six equations written above with proper syntax];
end

Answer 3

[Walter Roberson]

You are passing more than two values to bvpinit(). There is no bvpinit() syntax defined for six parameters, so possibly anything beyond the third parameter is being ignored. The three-parameter form of bvpinit() initializes the 'parameters' field of solinit. Then in the bvp4c() call, if the 'parameters' field of solinit is defined, then your ode function must accept 3 arguments, but your ode function myodesubfunc only accepts two arguments, leading to the error about two many input arguments.

I would suspect your bvpinit() call is incorrect.

Answer 4

[eh]

Hi I want to solve system of coupler ODEs in ode45 my boundary condition :: Some conditions are initially And others in end . can you helpe mi to enter boundary condition???

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