## HPL Errata - Bugs

### Issues fixed in Version 2.1, October 26th, 2012

The output now reports exact time stamps before and after the
execution of the solver function pdgesv() was run. This could
allow for accurate accounting of running time for data center
management purposes. For example as reporting power
consumption. This is important for the Green500 project.

Fixed an out-of-bounds access to arrays in the HPL_spreadN()
and HPL_spreadT() functions. This may cause segmentation
fault signals. It was reported by Stephen Whalen from Cray.

### Issues fixed in Version 2.0, September 10th, 2008

Gregory Bauer found a problem size corresponding to the
periodicity of the pseudo-random matrix generator used in the
HPL timing program. This causes the LU factorization to
detect the singularity of the input matrix as it should have.

A problem size of 2^17 = 131072 causes columns 14 modulo 2^14
(i.e. 16384) (starting from 0) to be bitwise identical on a
homogeneous platform. Every problem size being a power of 2
and larger than 2^15 will feature a similar problem if one
searches far enough in the columns of the square input matrix.

The pseudo-random generator uses the linear congruential
algorithm: X(n+1) = (a * X(n) + c) mod m as described in the
Art of Computer Programming, Knuth 1973, Vol. 2. In the HPL
case, m is set to 2^31.

It is very important to realize that this issue is a problem
of the testing part of the HPL software. The numerical
properties of the algorithms used in the factorization and
the solve should not be questioned because of this. In fact,
this is just the opposite: the factorization demonstrated the
weakness of the testing part of the software by detecting the
singularity of the input matrix.

This issue of the testing program is not easy to fix. This
pseudo-random generator has very useful properties despite
this. It is thus currently recommended to HPL users willing
to test matrices of size larger than 2^15 to not use power
twos.

This issue has been fixed by changing the pseudo-random
matrix generator. Now the periodicity of the generator is
2^64.

### Issues fixed in Version 1.0b, December 15th, 2004

When the matrix size is such that one needs more than 16 GB
per MPI rank, the intermediate calculation (mat.ld+1) *
mat.nq in HPL_pdtest.c ends up overflowing because it is
done using 32-bit arithmetic. This issue has been fixed by
typecasting to size_t; Thanks to John Baron.

### Issues fixed in Version 1.0a, January 20th, 2004

The MPI process grid numbering scheme defaults now to row-
major ordering. This option can now be selected at run time.

The inlined assembly timer routine that was causing the
compilation to fail when using gcc version 3.3 and above has
been removed from the package.

Various building problems on the T3E have been fixed; Thanks
to Edward Anderson.

### Issues fixed in Version 1.0, September 27th, 2000

Due to a couple errors spotted in the VSIPL port of the
software, the distribution contained in the tar file of
September 9th, 2000 had been updated on September 27th, 2000
with a corrected distribution. **These problems were
not affecting in any way possible the BLAS version of the
software.** If you are using the VSIPL port of HPL,
and want to make sure you are indeed using the latest
corrected version, please check the date contained in the
file HPL.build.log contained in the main directory.

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