How do you pass a matrix (parameter) to decic and ode15i?

Hello,

I am using ode15i, with decic to determine consistent initial conditions for a differential equation that involves a matrix. However, when I call these functions, I want to be able to input my matrix at the same time. That is, everything works perfectly if I have my function fun(t,x,xprime), and solve it using:

[xhat,y]=decic(@fun,0,v,v,w,w), (where v and w are vectors).

[t,x]=ode15i(@fun,[0,1],xhat,y);

But I want to be able to add a matrix input in "fun" (so that it is called with fun(C,t,x,xprime), so I am looking for something like

decic(@fun,C,0,v,v,w,w)

[t,x]=ode15i(@fun,C,[0,1],xhat,y)

where C is some matrix that I have defined earlier in the command window. This syntax does not work though ("not enough input arguments"). How do I input a previously defined matrix into a function within decic/ode15i?

Thanks!

Answer 1

[John Chilleri]

Hello,

Rather than having to include your matrix in the decic/ode15i functions as an input, you could declare your matrix as a global variable, and access it in your function fun.

If you haven't heard of global variables, you can find information here.

Example:

global C
C = some matrix you have;
Call ode15i as normal;

And,

function outputs = fun(t,x)
    global C
    Use C as needed;
end

Hope this helps!

[Bill Smythe]

Very helpful. Worked perfectly. Thank you very much!

[Walter Roberson]

Ick! Globals are slow, not a good idea for a routine that will have to be called many times. Parameterizing your function is much more efficient.

Answer 2

[Steven Lord]

Use the techniques described on this documentation page that is linked from the documentation page for ode15i (and the rest of the ODE solvers,)