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Torsten
Posts:
1,472
Registered:
11/8/10


Re: (yet unsolved) how to Solve coupled ODEs
Posted:
Feb 13, 2013 4:11 AM


"Henry" wrote in message <kfeavo$2f$1@newscl01ah.mathworks.com>... > I modified the code to: > > tspan = linspace(1, 2,100); > y = 0.0001*ones(1,200); > [T,sols] = ode45(@yprime, tspan,y); > and > dyds = [dyds1' ; dyds2']; > > and it now runs, thanks. > > But I have this question: My odes are timeindependent, function of "s" which is a distance, but since the ode45 will not work without a tspan, I came up with an arbitrary tspan. It looks as if ode45 interprets that "s" is a time? I'm confused as to how interpret the result of the routine which has dimensions of 100x200. I was expecting 1 x 200, i.e. independent of time. > thanks
By the way: I suspect that you want to set different values of a,b,c and d for different values of s and solve for only _two_ solutions y(1) and y(2). That's not what you do in your code above. You will have to use MATLAB's interp1 function to get values for a,b,c and d at the distance s where the solver needs the values of the derivatives dyds(1) and dyds(2).
Or do you want to make a parameter study, i.e. different solutions for different combinations of the parameters a,b,c and d ? Then your code above is also incorrect because you always refer to y(1) and y(2) in the evaluation of the derivatives, thus the solution for only the _first_ parameter set.
We need more information about your underlying problem in order to give useful advice.
Best wishes Torsten.



