[Numpy-tickets] [NumPy] #638: var should take absolute value for complex numbers.

NumPy numpy-tickets@scipy....
Sat Dec 29 22:17:35 CST 2007


#638: var should take absolute value for complex numbers.
-------------------------+--------------------------------------------------
 Reporter:  akumar       |        Owner:  somebody
     Type:  defect       |       Status:  new     
 Priority:  normal       |    Milestone:  1.0.5   
Component:  numpy.core   |      Version:  none    
 Severity:  normal       |   Resolution:          
 Keywords:  var complex  |  
-------------------------+--------------------------------------------------
Comment (by akumar):

 Replying to [ticket:638 akumar]:
 > Hi!
 >
 > I was just wondering why numpy.var gives me complex variances for
 complex numbers.
 >
 > e.g.
 >
 > {{{
 > h1 = (randn(1000,1) + 1j *randn(1000,1)) / sqrt(2)
 > var(h1)
 > }}}
 > gives: {{{ (-0.00757596036094-0.0234608549341j) }}}
 >
 > While I actually expect the output to be similar to that which is from
 > {{{
 > var(square(abs(h1)))
 > }}}

 Wrong! Actually, it should be {{{ mean(square(abs(h1))) }}}
 which gives: {{{ 995184304741 }}}

 Thanks.

 Kumar

-- 
Ticket URL: <http://scipy.org/scipy/numpy/ticket/638#comment:1>
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