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2020-08-05 06:56:27 -0500 received badge  Popular Question (source)
2019-06-26 05:21:03 -0500 asked a question Compute the square root of a complex matrix

Hello,

I can't find how to compute the square root of a complex matrix... I tried m.sqrt(), sqrt(m) (display only symbolic sqrt), sqrt(m).n()... None of them work. What is the regular way to compute the root of a complex matrix? (you can assume the matrix is self-adjoint if needed).

Thanks!

def test():
    phi = matrix(CC, [[1/sqrt(2)],[i]])
    m = phi * phi.C.T
    print("Matrix: {}".format(m))
    s = sqrt(m).n() # Does not work: AttributeError: 'ComplexField_class_with_category' object has no attribute 'complex_field'
    #s = m^(1/2) # Does not work either, NotImplementedError: non-integral exponents not supported
    # s = m.sqrt() # Does not work either, no attribute sqrt
    print("Sqrt: {}".format(s))
    print("s*s: {}".format(s*s))
    if s*s == m:
        print("Ok")
    else:
        print("Nope :(")

EDIT: For now I'm using the numpy backend with manual diagonalisation, but I'd like to know if there is a better way to proceed...

 phi = matrix(CDF, [[1/sqrt(2)],[i]])
 D, P = m.eigenmatrix_right()
 s = P*diagonal_matrix([sqrt(x) for x in D.diagonal()])*P^-1
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2018-04-16 02:57:45 -0500 asked a question Square root of polynomial modulo another irreducible polynomial

Hello,

If I'm not wrong, it is always possible to compute the square root of a polynomial $P$ modulo an irreducible polynomial $g$ when the base field is in $GF(2^m)$, i.e. find $Q \in GF(2^m)$ such that $Q^2 \equiv P \mod g$. Indeed, the operation $Q \rightarrow Q^2 \pmod g$ should be linear (because we are in $GF(2^m)$) so an idea would be to compute the matrix $T$ that perform this operation, and then invert it, but I'd like to find an embedded operation in sage. I tried the sagemath $P.sqrt()$ method, but the problem is that because it does not take into account the modulo, it fails most of the time when the polynomial has some terms with odd power of $X$.

Any idea?

Thanks!

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2018-04-16 02:46:37 -0500 commented answer Map a matrix to a block matrix

Ok, thank you for your help !

2018-04-10 17:15:48 -0500 asked a question Map a matrix to a block matrix

Hello,

I have a function that maps an element $x$ into a $1\times n$ matrix, say for example $[x,x,x]$. I would like to map this function to a matrix and consider the resulting matrix as a "block matrix". E.g: change matrix([[1,2],[3,4]]) into matrix([[1,1,1,2,2,2],[3,3,3,4,4,4]]).

For now, I use a trick that basically converts back the matrix to a a list using something like:

block_matrix([[f(elt) for elt in row] for row in M.rows()])

but it looks quite dirty so I would like to know if there are some better way to proceed.

Thank you!

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2013-06-10 10:02:53 -0500 asked a question Choose the viewpoint in plot3d

Hello,

I would like to display lots of spheres (about 6000) in jmol but when I've to many points it crashs.

If I try to run the interactive mode (even If don't have any picture) I've this error : "Jmol Applet #2 is having trouble loading. Will retry once."

How could I do to get a picture of my work ?

--- EDIT ---

I found the function save('filename') and now I've a display, but I'd like to change the point of view. Is it possible ?

Thanks,

Tobias.