Convert function handle to a function in ODE45

Question

Sattik Basu 2022-12-2

回答： Walter Roberson 2022-12-3

Suppose I have a symbolic matrix J

J = [2*y(1), 4*y(2), y(1)*y(2);
     y(3), 2*y(1)^2, 5*y(2);
     5*y(3), 2*y(2)*y(1), 2*y(2)];

I can convert it to a function handle using

Jnew = matlabFunction(J)

So now it shows as Jnew = @(y(1),y(2),...)reshape([.....],[3,3]

The issue begins now. Since I want this J to be used in an ode45 environment. For example

[T,Y] = ode45(@(t,y) myode(t,y,Jnew), span, IC)

where myode is

function dy = myode(t,y,J)
vars = y(1:3)
A = [1 2 3;
     1 3 4;
     7 6 5];
dy = A*vars + J*vars;
end

How can I use J as an input here?

Answer 1

Walter Roberson 2022-12-3

Do not do that. Instead use

A = [1 2 3;
     1 3 4;
     7 6 5];
Jnew = matlabFunction(A*y(:) + J*y(:), 'vars', {y(:)});
[T,Y] = ode45(Jnew, span, IC)