MATLAB: ‘subs’ not working as i want

MATLABmatrixsubs

Hello guys,

I have this equation -x^2/2 + 2*x – (5*I)/2 and I'm trying to replace the letter x with a the matrix A and the letter I with the matrix B.

A = 0 1 0

0 0 1

2 -5 4

B = eye(3)

The problem is that when I write subs(eq, x, A) and subs(eq, I, eye(3)) I get a very big matrix, and this is not the answer.

Do both subs at the same time

subs(eq, {x, I}, {A, eye(3)})

Symfun is a subclass of sym, so, yes, a symfun is already a sym.

To get only the body of the function, use formula or call the symfun:

syms x(t)
x(t) = t^2 - t;
formula(x)
% or:
x(t)

variant without symbolic toolbox

a = arrayfun(@(x)p^x*yu,0:2,'un',0);
rt = sum([a{:}],2)