python power operator strange behaviour

Asked May 24 '14 at 14:03

Active May 24 '14 at 14:07

Viewed 35 times

I am trying to implement multivariate gaussian pdf. I have a strange issue with the ** operator.The code is

def multi_var(x,mu,cov):
   #Multivariate gaussian
   print (1/2*np.pi)**(len(x)/2)
   return(((1/2*np.pi)**(len(x)/2))/np.sqrt(np.abs(np.linalg.det(cov)))*np.exp(np.dot(np.matrix.transpose(x-mu),np.dot(np.linalg.inv(cov),(x-mu)))))

In the command it gives

>>> print multi_var(np.matrix('0;0;4'),np.matrix('0;0;6'),np.matrix([[.3,.67,8],[2,3,8],    [2,.05,2]]))
2
[[ 0.]]

When I execute the same code from command line

>>> x=np.matrix('0;0;4')
>>> print (1/2*np.pi)**(len(x)/2)

I get

 1.96870124322

edited May 24 '14 at 14:07

Martijn Pieters

1,048,767
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asked May 24 '14 at 14:03

user3443615

1

In Python 2, `1/2` and `len(x) / 2` uses *integer division*, is that intentional? – Martijn Pieters May 24 '14 at 14:05
Yes,this is python 2.7, spyder IDE from Anaconda stack – user3443615 May 24 '14 at 14:07
`1/2` is `0` unless you use float division. – Martijn Pieters May 24 '14 at 14:08
No, But in command line it works well,why in script?? that solved the problem anyway thanks... – user3443615 May 24 '14 at 14:10
Most likely because your command line is Python 3, not Python 2. – Martijn Pieters May 24 '14 at 14:12

python power operator strange behaviour

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