On Fri, Feb 29, 2008 at 12:24 PM, Dan Christensen <[EMAIL PROTECTED]> wrote:
> In numpy:
>
> In [11]: A[2:4]
> Out[11]:
> array([[ 1, 1, 2, -1],
> [ 2, -1, 1, -1]])
>
> (Or A[2:4,0:4].)
>
>
> >>> # a column
> >>> sage: A.matrix_from_rows_and_columns([1..2],[0..0])
> >>> [14]
> >>> [ 1]
>
> In numpy it's A[1:3,0].
SAGE now tries to support numpy (and matlab)-style indexing, by poking
at its underlying __getitem__ and __getslice__ (thanks to a suggestion
by William):
{{{
sage: m=[(1, -2, -1, -1,9), (1, 8, 6, 2,2), (1, 1, -1, 1,4), (-1, 2,
-2, -1,4)];M= matrix(m)
sage: M
[ 1 -2 -1 -1 9]
[ 1 8 6 2 2]
[ 1 1 -1 1 4]
[-1 2 -2 -1 4]
Get The 2 x 2 submatrix of M, starting at row index and column
index 1
sage: M[1:3,1:3]
[ 8 6]
[ 1 -1]
Get the 2 x 3 submatrix of M starting at row index and column
index 1:
sage: M[1:3,[1..3]]
[ 8 6 2]
[ 1 -1 1]
Get the second column of M:
sage: M[1:,0]
[ 1]
[ 1]
[-1]
sage: M[range(2),:]
[ 1 -2 -1 -1 9]
[ 1 8 6 2 2]
sage: M[range(2),4]
[9]
[2]
sage: M[range(3),range(5)]
[ 1 -2 -1 -1 9]
[ 1 8 6 2 2]
[ 1 1 -1 1 4]
sage: M[3,range(5)]
[-1 2 -2 -1 4]
sage: M[3,:]
[-1 2 -2 -1 4]
sage: M[3,4]
4
}}}
Please review the patch at
http://trac.sagemath.org/sage_trac/ticket/2355 and help me shake out
any bugs that I might have missed or possible speedups, etc.
I guess it's safe to erase the submatrix command, although we could
make it call __getitem__ if we chose to keep it. Thoughts?
didier
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