# Problem with ODE45

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Commented: Richard Brown on 7 Nov 2019
I should solve 2 coupled matrix differential equations. for that, I have created a script (m-file) in which I have defined all matrices with constant values. I have also created another script for a function and call this function in the first m-file. Finally I have used ode45 to solve the function, but it doesn't work!
The systom to be solved (A, L, R and P are matrices with constant components):
My function (which its name is 'myode'):
function dydt=myode(t,y,A,R,L,P)
[m n]=size(P);
[k l]=size(L);
for a=1:m
dydt(a)=P(a,:)*y(a);
end
for b=1:k
dydt(m+b)=inv(L)*(A*y(m+b)-R*y(b));
end
end
My first script (m-file):
tspan=linspace(5,5.010,11);
i_0=transpose([0.355 -0.355 2.046 0.711 0 0.709]);
u_0=transpose([1002.40 1001.98 1012.04 986.11]);
y0=[u_0;i_0];
[T Y]=ode45(@(t,y) myode(t,y,A,R,L,P),tspan,y0)
==> but when I run my first script, the following error pops up:
Error in Test>@(t,y)myode(t,y,A,R,L,P)
Error in odearguments (line 87)
f0 = feval(ode,t0,y0,args{:}); % ODE15I sets args{1} to yp0.
Error in ode23 (line 114)
odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);
Error in Test (line 58)
[T Y]=ode23(@(t,y) myode(t,y,A,R,L,P),tspan,y0)
Anyone has an idea what the problem is?
Richard Brown on 7 Nov 2019
You're definitely going to have issues trying to build your derivative one term at a time (look at the term involvint inv(L) for a start). why can't you just do the following?
function dydt=myode(t,y,A,R,L,P)
u = y(1:3);
i = y(4:7);
dydt = [L\(A*u - R*i); P*i];
end
will be much easier to troubleshoot.

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