Status: Accepted
Owner: asmeurer
Labels: Type-Defect Priority-Medium Matrices
New issue 2212 by asmeurer: Matrix([Matrix, …]) should work
http://code.google.com/p/sympy/issues/detail?id=2212
Here is my Matrix:
In [49]: a
Out[49]:
⎡1 -1 1 -1 1 -1 1 -1 1 ⎤
⎢ ⎥
⎢2 0 -1 -2 0 1 2 0 -1⎥
⎢ ⎥
⎢4 0 -2 0 0 0 -2 0 1 ⎥
⎢ ⎥
⎢2 2 2 0 0 0 -1 -1 -1⎥
⎢ ⎥
⎣1 1 1 1 1 1 1 1 1 ⎦
I want to construct the matrix
In [46]: b
Out[46]:
⎡1 -2 2 1 -2 1 ⎤
⎢ ⎥
⎢2 -2 1 0 1 -1⎥
⎢ ⎥
⎢4 0 -4 0 0 1 ⎥
⎢ ⎥
⎢2 2 1 0 -1 -1⎥
⎢ ⎥
⎣1 2 2 1 2 1 ⎦
which is a except the fourth column has been removed and added to the
third, the seventh column has been removed and added to the third, and the
eight column has been removed and added to the sixth (the matrix a
represents the coefficients of partial derivatives with respect to (x1,
x1), (x1, x2), (x1, x3), (x2, x1), etc., so for example, the partial with
respect to (x2, x1) can just be added to the partial with respect to (x1,
x2) and removed).
Now, I would have liked to have been able to do something like
b = Matrix(a[:,0], a[:,1] + a[:,3], a[:,2] + a[:,-3], a[:,4], a[:,5] +
a[:,-2], a[:,-1])
or
b = Matrix([a[:,0], a[:,1] + a[:,3], a[:,2] + a[:,-3], a[:,4], a[:,5] +
a[:,-2], a[:,-1]])
but those didn't work. In fact,
b = Matrix([a[:,0].T, a[:,1].T + a[:,3].T, a[:,2].T + a[:,-3].T, a[:,4].T,
a[:,5].T + a[:,-2].T, a[:,-1].T]).T
didn't even work. The only that worked in the end was
b = Matrix([list(a[:,0].T), list(a[:,1].T + a[:,3].T), list(a[:,2].T +
a[:,-3].T), list(a[:,4].T), list(a[:,5].T + a[:,-2].T), list(a[:,-1].T)]).T
Now, I don't know which of the above are consistent syntactically speaking,
but it seems to me that at least the one without the list() calls should
work (it would be nice if the first one worked too, but someone with a
better handle on how this Matrix syntax should work should have a say on
that).
P.S., is there a method of Matrix that would have made this easier to
construct?
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