[Numpy-discussion] Segfault with QR Decomposition

[Charanpal Dhanjal]

> >/ I get a segmentation fault upon running the following:
> />/
> />/ import numpy
> />/ A = numpy.ones((7000000, 8))
> />/ Q, R = numpy.linalg.qr(A)
> />/
> />/ on Python 2.7.3, Linux 64-bit using numpy 1.9.0.dev-ec3603f linked
> />/ against OpenBLAS. If A is a smaller matrix then the QR decomposition
> />/ works (for example A has shape (4000000, 8)). I haven't quite narrowed
> />/ down the exact threshold where the crash occurs, however I know that the
> />/ above A is 448 MB (Q and R are no bigger), and the machine in question
> />/ has 32GB of RAM. I also tested scipy.linalg.qr (version
> />/ 0.14.0.dev-ced994c) with the same results.
> />/
> />/ I don't get the same problem on my laptop which is Python 2.7.3, Linux
> />/ 64-bit but with numpy 1.8.0rc1 linked to OpenBLAS. Both machines have
> />/ OpenBLAS 0.2.6. Does anyone have some insight into why this problem is
> />/ occuring?
> />/
> />/
> /Works fine here with '1.9.0.dev-7457f15' linked against ATLAS. I suspect
> problem is in OpenBLAS. What architecture/os do the two machines have? Is
> OpenBLAS using more than one core?

Thanks for testing the code. On the desktop machine I am using Debian GNU/Linux 7.2 (wheezy) compiled for x86-64 (Intel(R) Xeon(R) CPU E5-1620), and on my laptop I use Ubuntu 13.04 for x86-64 (Intel(R) Core(TM) i7-3740QM). I tried: 

export OPENBLAS_NUM_THREADS=1

and 

export OPENBLAS_NUM_THREADS=1

with the same results (a segfault). 

Charanpal 

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