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element-wise operations

asked 2013-11-10 05:47:44 -0500

gundamlh gravatar image

In MATLAB element-wise operations:

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".*", ".^", "./" and so on.

In SAGE I have only found ".elementwise_product()". Are there any other element-wise operations on matrices, vectors, lists?

Thanks in advance!

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answered 2013-11-10 06:55:19 -0500

tmonteil gravatar image

updated 2013-11-10 07:00:24 -0500

For lists, you can use list comprehension or the map function:

sage: [M[i] + N[i] for i in xrange(len(M))]
sage: map(operator.add, N, M)

For matrices, there is no such mechanism out of the box, but you can make one by yourself as follows:

def elementwise(operator, M, N):
    assert(M.parent() == N.parent())
    nc, nr = M.ncols(), M.nrows()
    A = copy(M.parent().zero_element())
    for r in xrange(nr):
        for c in xrange(nc):
            A[r,c] = operator(M[r,c], N[r,c])
    return A

and then use it as follows:

sage: elementwise(operator.add, M, N)
sage: elementwise(operator.pow, M, N)
sage: elementwise(operator.mul, M, N)
sage: elementwise(operator.div, M, N)

and so on.

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Orz, so quick. Thanks

gundamlh gravatar imagegundamlh ( 2013-11-10 07:15:34 -0500 )edit

assert() is perhaps not a good choice for element-wise division? And why do you use xrange(), but not range()?

gundamlh gravatar imagegundamlh ( 2013-11-10 23:33:44 -0500 )edit

I believe that numpy arrays will do this automatically, however. Sage is built around mathematical constructs, but you can use Numpy from within Sage to do this.

kcrisman gravatar imagekcrisman ( 2013-11-11 04:25:44 -0500 )edit

Thanks! I am starting to learn NumPy.

gundamlh gravatar imagegundamlh ( 2013-11-22 04:46:57 -0500 )edit

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Asked: 2013-11-10 05:47:44 -0500

Seen: 1,095 times

Last updated: Nov 10 '13