Extract matrices out of a symbolic matrix

Let's assume I have a matrix which looks something like:

    Mtx = [2,3*x;4*x^2,1]

Is it "symbolically" possible to get 3 matrices out of this, which look like:

    Mtx1 = [2,0;0,1]

    Mtx2 = [0,3*x;0,0]

    Mtx3 = [0,0;4*x^2,0]

Is there a function, that can do this or should I do it manually?

Answer 1

[Andrew Newell]

It looks like you are trying to extract the diagonal, upper triangular and lower triangular parts of the matrix. These commands will do it for larger matrices as well:

Mtx1 = diag(diag(Mtx));
Mtx2 = triu(Mtx,1);
Mtx3 = tril(Mtx,-1);

[Ahmed Hossam]

Thanks for your answer! What I am actually trying to do here is to extract the matrices depending on x^0 or x^1 or x^2 ... Because I have a matrix, where I don't actually now, where the terms are exactly located ...

[Andrew Newell]

O.k., for the example you have given, this will do it:

syms x
Mtx = [2,3*x;4*x^2,1];
Mt3 = diff(Mtx,x,2)*x^2/2;
Mt2 = diff(Mtx-Mt3,x,1)*x;
Mt1 = Mtx-Mt2-Mt3;

It would be straightforward to generalize this to higher derivatives, remembering that for the nth derivative you have to divide by n factorial.

[Ahmed Hossam]

you're right!