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Matrix Multiplication

asked 2010-12-28 11:15:18 -0500

mhfrey gravatar image

updated 2010-12-28 11:40:58 -0500

Mike Hansen gravatar image

I am trying to multiply the following:


This should work, what am I doing wrong? I would expect (1/2, 0)

Sage returns the following error:

Traceback (click to the left of this block for traceback)
TypeError: 'sage.matrix.matrix_rational_dense.Matrix_rational_dense'
object cannot be interpreted as an index

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "", line 10, in <module>
    exec compile(u'open("","w").write("# -*- coding: utf-8 -*-\\n" +    _support_.preparse_worksheet_cell(base64.b64decode("SXo9MS8yKm1hdHJpeCgyLDIsW1sxLDBdLFswLC0xXV0pO0l6CmE9KDEsMCkKSXoqYQ=="),globals())+"\\n"); execfile(os.path.abspath(""))
  File "", line 1, in <module>

  File "/tmp/tmpJoBb2Y/", line 5, in <module>
    exec compile(u'Iz*a
  File "", line 1, in <module>

  File "element.pyx", line 2260, in sage.structure.element.Matrix.__mul__     (sage/structure/element.c:14881)
  File "coerce.pyx", line 759, in sage.structure.coerce.CoercionModel_cache_maps.bin_op (sage/structure/coerce.c:6940)
TypeError: 'sage.matrix.matrix_rational_dense.Matrix_rational_dense' object cannot be interpreted as an index


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2 answers

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answered 2010-12-28 11:44:37 -0500

Mike Hansen gravatar image

The issue is that when you do a = (1,0) you are creating a tuple which is one of Python's built-in data types.

sage: type((1,0))
<type 'tuple'>

Sage doesn't "know" how to multiply a matrix and a tuple.

If you make a a vector instead, then thing will work like you want:

sage: Iz=1/2*matrix(2,2,[[1,0],[0,-1]])
sage: a = vector([1,0])
sage: type(a)
<type 'sage.modules.vector_rational_dense.Vector_rational_dense'>
sage: Iz * a
(1/2, 0)
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answered 2010-12-28 13:35:54 -0500

mhfrey gravatar image

That works, thank you for the quick answer.

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If you want to, you can accept Mike's answer, so that other users know this question was answered correctly when they search for a similar problem!

kcrisman gravatar imagekcrisman ( 2011-01-03 15:03:09 -0500 )edit

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Asked: 2010-12-28 11:15:18 -0500

Seen: 1,426 times

Last updated: Dec 28 '10