reassign 569436 lapack 3.2.1-2 severity 569436 grave thanks On Thu, Feb 11, 2010 at 08:02:21PM +0100, Lucas Nussbaum wrote: > During a rebuild of all packages in sid, your package failed to build on > amd64. > > Relevant part: > > make[3]: Entering directory > > `/build/user-libitpp_4.0.7-1-amd64-Zz34fy/libitpp-4.0.7/tests' [snip] > > ------------------------------------------------------------------------------ > > Test `svd_test' FAILED!!! > > ------------------------------------------------------------------------------
Lucas, thanks for the bug report. I investigated the cause of this bug, and it appears that the SVD does, indeed, give a wrong result. Since the SVD is done by Lapack's zgesvd function, I reassign the bug report to Lapack, and set the severity to grave, since several programs such as Octave also use this function (Indeed, I did verify that Octave also produces incorrect results). Lapack maintainers, here are a few methods by which you can reproduce the error. - I used an example program from Intel, which I don't attach here since it is copyrighted: http://software.intel.com/sites/products/documentation/hpc/mkl/lapack/mkl_lapack_examples/zgesvd_ex.f.htm The program lists the expected output. Indeed, the output is correct in a Lenny system, but it is wrong in my chroot, where the FTBFS happens. There, I get the output as: ( -0.86, 0.00) ( 0.40, 0.00) ( 0.32, 0.00) ( -0.35, -0.21) ( -0.24, -0.21) ( -0.63, 0.60) ( 0.15, 0.61) ( 0.61, 0.61) ( -0.36, 0.10) which differs from the output given within the code. - I used Octave in the chroot, and compared it with a "working" Octave, for this: A = [1 2 3; 4 5 6; 7 8 9] * 1j; [U, S, V] = svd(A); disp(U); The correct U is: -0.000000 - 0.214837i -0.000000 - 0.887231i -0.402839 - 0.066237i 0.000000 - 0.520587i 0.000000 - 0.249644i 0.805678 + 0.132474i 0.000000 - 0.826338i 0.000000 + 0.387943i -0.402839 - 0.066237i But in the chroot, I get: -0.00000 - 0.88741i -0.00000 - 0.88723i -0.39566 - 0.10061i 0.00000 - 0.25007i -0.00000 - 0.24964i 0.79131 + 0.20122i 0.00000 + 0.38726i 0.00000 + 0.38794i -0.39566 - 0.10061i Again, I don't think the net fault lies with lapack, since libitpp built and passed all tests on the buildds with this very version of lapack; I couldn't think of what changes caused this to happen, though. Please let me know what else I can do to help. Thanks! Kumar -- If you shed tears when you miss the sun, you also miss the stars. - Rabindranath Tagore (Stray Birds, 1916)
signature.asc
Description: Digital signature
