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Extract matrices out of a symbolic matrix

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Ahmed Hossam
Ahmed Hossam 2017-4-20
评论： Ahmed Hossam 2017-4-28
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 2017-4-20
编辑：Andrew Newell 2017-4-20
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
Andrew Newell 2017-4-20
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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