Evaluate symbolic matrix numerically.

Hi,

I am trying to figure out how to evaluate a matrix that contains variables numerically.

For example:

syms A B;

matrix = [1-A, 1-B; 6*A, 10*B];

A = 0.5
B = 1.0
matrix

For me, this just displays:

A =

      0.5000

B =

       1

matrix =

[ 1 - A, 1 - B]
[   6*A,  10*B]

How can I get the matrix to be evaluated numerically with the newly defined numbers? This is an extremely simplified version of what I am trying to do. In my actual program, I am taking the jacobian of a matrix symbolically, and then I need to evaluate the matrix numerically, therefore in this small example, I cannot simply move A & B above the "matrix = [1-A, 1-B; 6*A, 10*B];" line. Basically, is there a way to evaluate a matrix numerically after assembling the matrix with variables?

Answer 1

[Jiro Doke]

Use subs:

subs(matrix, {A, B}, {0.5, 1})

[Manuel Escobar]

IT WORK! THANKS

[Mohamed Hajjaj]

If the matrix Phi is dependent on one parameter( say t), can I use Phi (T) to get the numeric value of Phi at numeric value T?

The below link may explain this question:

http://www.chebfun.org/examples/ode-linear/Floquet.html

at the following section:

[n,n1]=size(Phi);

PhiT = zeros(n);

for i = 1:n

for j = 1:n

PhiT(i,j) = Phi{i,j}(T);

end

end

B = logm(PhiT)/T;

Any help would be appreciated.