Evaluate symbolic matrix numerically.

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Andrew
Andrew 2011-4-17
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?

回答(1 个)

Jiro Doke
Jiro Doke 2011-4-17
Use subs:
subs(matrix, {A, B}, {0.5, 1})
  2 个评论
Mohamed Hajjaj
Mohamed Hajjaj 2021-4-16
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:
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.

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