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

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Bill Smythe on 22 Jan 2017
Commented: Walter Roberson on 23 Jan 2017
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!

John Chilleri on 22 Jan 2017
Edited: John Chilleri on 22 Jan 2017
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!
##### 2 CommentsShowHide 1 older comment
Walter Roberson on 23 Jan 2017
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.

Steven Lord on 23 Jan 2017
Use the techniques described on this documentation page that is linked from the documentation page for ode15i (and the rest of the ODE solvers,)

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