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<TITLE>HPL Errata-Bugs</TITLE> |
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<H2>HPL Errata - Bugs</H2> |
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<H3>Issues fixed in Version 2.0, September 10th, 2008</H3> |
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Gregory Bauer found a problem size corresponding to the |
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periodicity of the pseudo-random matrix generator used in the |
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HPL timing program. This causes the LU factorization to |
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detect the singularity of the input matrix as it should have.<BR><BR> |
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A problem size of 2^17 = 131072 causes columns 14 modulo 2^14 |
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(i.e. 16384) (starting from 0) to be bitwise identical on a |
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homogeneous platform. Every problem size being a power of 2 |
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and larger than 2^15 will feature a similar problem if one |
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searches far enough in the columns of the square input matrix.<BR><BR> |
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The pseudo-random generator uses the linear congruential |
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algorithm: X(n+1) = (a * X(n) + c) mod m as described in the |
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Art of Computer Programming, Knuth 1973, Vol. 2. In the HPL |
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case, m is set to 2^31.<BR><BR> |
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It is very important to realize that this issue is a problem |
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of the testing part of the HPL software. The numerical |
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properties of the algorithms used in the factorization and |
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the solve should not be questioned because of this. In fact, |
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this is just the opposite: the factorization demonstrated the |
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weakness of the testing part of the software by detecting the |
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singularity of the input matrix.<BR><BR> |
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This issue of the testing program is not easy to fix. This |
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pseudo-random generator has very useful properties despite |
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this. It is thus currently recommended to HPL users willing |
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to test matrices of size larger than 2^15 to not use power |
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twos.<BR><BR> |
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This issue has been fixed by changing the pseudo-random |
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matrix generator. Now the periodicity of the generator is |
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2^64.<BR><BR> |
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<H3>Issues fixed in Version 1.0b, December 15th, 2004</H3> |
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When the matrix size is such that one needs more than 16 GB |
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per MPI rank, the intermediate calculation (mat.ld+1) * |
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mat.nq in HPL_pdtest.c ends up overflowing because it is |
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done using 32-bit arithmetic. This issue has been fixed by |
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typecasting to size_t; Thanks to John Baron.<BR><BR> |
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<H3>Issues fixed in Version 1.0a, January 20th, 2004</H3> |
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The MPI process grid numbering scheme defaults now to row- |
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major ordering. This option can now be selected at run time.<BR><BR> |
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The inlined assembly timer routine that was causing the |
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compilation to fail when using gcc version 3.3 and above has |
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been removed from the package.<BR><BR> |
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Various building problems on the T3E have been fixed; Thanks |
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to Edward Anderson.<BR><BR> |
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<H3>Issues fixed in Version 1.0, September 27th, 2000</H3> |
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Due to a couple errors spotted in the VSIPL port of the |
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software, the distribution contained in the tar file of |
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September 9th, 2000 had been updated on September 27th, 2000 |
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with a corrected distribution. <STRONG>These problems were
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not affecting in any way possible the BLAS version of the |
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software.</STRONG> If you are using the VSIPL port of HPL,
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and want to make sure you are indeed using the latest |
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corrected version, please check the date contained in the |
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file HPL.build.log contained in the main directory.<BR><BR> |
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