[Numpy-discussion] matrixmultiply problem

Geoffrey Philbrick geoffp at rochester.rr.com
Wed Aug 11 20:08:09 CDT 2004


Executing the following code has the side effect of modifying one of the arguments (matrices) I passed to matrixmultiply. Note that the matrix m2 changes after the call to matrixmultiply. This is on Windows with numarray 1.0. 

Why does this happen?

Code:

from numarray import array, matrixmultiply

m1 = array(
[[ 1., 0., 0.],
[ 0., 1., 0.],
[ 0., 0., 1.]]
)

m2 = array(
[[ 0.500011, 0.86601905, 0. ],
[-0.86601905, 0.500011, 0. ],
[ 0., 0., 1. ]]
)

print "m1 before\n", m1
print "m2 before\n", m2
matrixmultiply(m1, m2)
print "m1 after\n", m1
print "m2 after\n", m2

Output:

m1 before
[[ 1. 0. 0.]
[ 0. 1. 0.]
[ 0. 0. 1.]]
m2 before
[[ 0.500011 0.86601905 0. ]
[-0.86601905 0.500011 0. ]
[ 0. 0. 1. ]]
m1 after
[[ 1. 0. 0.]
[ 0. 1. 0.]
[ 0. 0. 1.]]
m2 after
[[ 0.500011 -0.86601905 0. ]
[ 0.86601905 0.500011 0. ]
[ 0. 0. 1. ]]



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