[Numpy-discussion] Matrix times scalar is wacky

Alan G Isaac aisaac at american.edu
Fri Feb 24 06:15:12 CST 2006


On Fri, 24 Feb 2006, Bill Baxter apparently wrote: 
> Multiplying a matrix times a scalar seems to return junk for some reason: 

Confirmed.
Alan Isaac

Python 2.4.1 (#65, Mar 30 2005, 09:13:57) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as N
>>> N.__version__
'0.9.5'
>>> a=N.array([[1,2],[3,4]],'f')
>>> b=N.mat(a)
>>> a*0.2
array([[ 0.2       ,  0.40000001],
       [ 0.60000002,  0.80000001]], dtype=float32)

#this works ok

>>> b*0.2
matrix([[ 0.2,  0.4],
       [ 0.6,  0.8]])

>>> a = N.rand(1,2)
>>> b = N.mat(a)
>>> a*0.2
array([[ 0.01992175,  0.09690914]])

# this does not work ok

>>> b*0.2
matrix([[  1.99217540e-002,   2.22617305e-309]])
>>>





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