CODEWITHSUNDEEP
pythonjupyter-notebookipython
Oscar Campo
Oscar Campo

Reputation: 3

Wrong result in a simple ipython script

I defined a simple function that operates on 1st and 3rd rows of a 3x3 matrix:

In [1]: from numpy import *    
     from sympy import Symbol
 
In [2]: def ifsin(mat): 
     mat[2,:]+=1
     mat[0,:]=mat[0,:]/pow(mat[2,:],mat[2,:]>0)
     return mat
 
In [3]:Ay=Symbol('Ay')
     By=Symbol('By')
     q=array([[Ay,-10 ,By],[0,0.4,1],[-1 ,-1, -1]])
     q
 
Out[3]:
 
 array([[Ay, -10, By],
        [0, 0.4, 1],
        [-1, -1, -1]], dtype=object)
 
In [4]:V=ifsin(q)
        q
 
Out[4]: array([[Ay, -10.0, By],
        [0, 0.4, 1],
        [0, 0, 0]], dtype=object)

Why was updated 3rd row of matrix q?

Also if I eval following:

In [5]:M=ifsin(V)
       q
     
Out[5]: array([[Ay, -10.0, By],
            [0, 0.4, 1],
            [1, 1, 1]], dtype=object)

Again 3rd row of q is updated!!

I tried this script on "Computable" (ipad app) and ipython notebook on ubuntu 14.04 (python 2.7.6) with the same results

Thanks in advance for your help.

updated…

I changed my function to:

def ifsin(m): 
  return vstack([m[0,:]/pow(m[2,:]+1,(m[2,:]+1)>0),m[1,:],m[2,:]+1])

And now all works fine. Thanks!!

Upvotes: 0

Views: 73

Answers (1)

Oliver W.
Oliver W.

Reputation: 13459

You are literally asking for that update on this line:

mat[2,:]+=1

In numpy syntax, this means "update row 2 of the array named mat by incrementing each value by 1".

Upvotes: 1

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