Extract matrices out of a symbolic matrix
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Ahmed Hossam
on 20 Apr 2017
Commented: Ahmed Hossam
on 28 Apr 2017
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?
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Accepted Answer
Andrew Newell
on 20 Apr 2017
Edited: Andrew Newell
on 20 Apr 2017
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);
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Andrew Newell
on 20 Apr 2017
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.
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