[Numpy-discussion] segmentation fault

Charles R Harris charlesr.harris@gmail....
Wed May 28 11:58:03 CDT 2008


On Wed, May 28, 2008 at 10:39 AM, Stéfan van der Walt <stefan@sun.ac.za>
wrote:

> 2008/5/28 Hoyt Koepke <hoytak@gmail.com>:
> > In my experience tracking down these sorts of things, if the effect is
> > delayed and detected by glibc, it almost always means that a few bytes
> > beyond the end of the data part of an array have been overwritten.
> > This causes glibc's memory management stuff to crash later on when the
> > object is deallocated (or something like that).  Of course, I should
> > say I was doing the overwritting in my own c code...
>
> If you look at the valgrind trace I sent earlier, you'll see that that
> is the case.
>

It's shape related.

In [7]: x = numpy.random.rand(5,2)

In [8]: y = ones((5,2))

In [9]: x.cumsum(None,out=y)
Out[9]:
array([[ 0.76943981,  1.        ],
       [ 1.12678411,  1.        ],
       [ 1.69498328,  1.        ],
       [ 2.50560628,  1.        ],
       [ 3.23050034,  1.        ]])

In [10]: x.cumsum(None,out=x.reshape(10))
Out[10]:
array([ 0.76943981,  1.12678411,  1.69498328,  2.50560628,  3.23050034,
        3.82341732,  4.78267467,  4.94663937,  5.39959179,  5.94577506])

In [11]: x.cumsum(None,out=x.reshape(10))
Out[11]:
array([  0.76943981,   1.89622392,   3.5912072 ,   6.09681347,
         9.32731382,  13.15073114,  17.9334058 ,  22.88004517,
        28.27963696,  34.22541202])

In [12]: x.cumsum(None,out=x.reshape(10))
Out[12]:
array([   0.76943981,    2.66566373,    6.25687093,   12.3536844 ,
         21.68099822,   34.83172935,   52.76513516,   75.64518033,
        103.92481729,  138.1502293 ])

Chuck
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