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Extract matrices out of a symbolic matrix

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Ahmed Hossam
Ahmed Hossam el 20 de Abr. de 2017
Comentada: Ahmed Hossam el 28 de Abr. de 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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Andrew Newell
Andrew Newell el 20 de Abr. de 2017
Editada: Andrew Newell el 20 de Abr. de 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);
  3 comentarios
Andrew Newell
Andrew Newell el 20 de Abr. de 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.
Ahmed Hossam
Ahmed Hossam el 28 de Abr. de 2017
you're right!

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