Post here if you have a question about LAPACK or ScaLAPACK algorithm or data format


Postby akia313 » Tue Jan 27, 2015 7:31 am

Dear all,

I want to apply DLARFB on a part of a Matrix. I wrote this program but I think something is wrong, because the result is just 0,0 and 0. Could you please give an sample program that uses DLARFB?


function dormtr Intel MKL

Postby petergrant » Mon Feb 08, 2016 12:58 pm

I wrote several years ago that the algorithm of completion of Householders method in diagonalization of real symmetric matrices, implemented in Intel MKL package, can be improved significantly. This improvement is introduced now, and this is done cunningly: it is hidden inside the dormql (dormqr) Intel MKL function. When using the dormql (dormqr) function from Lapack package, the time of the computation increases. It corresponds to the use of dlarfb Intel MKL function (old algorithm is used). But even now, taking into account this improvement, the difference between the best diagonalization algorithms for square matrices from Intel MKL package and my diagonalization algorithm for packed matrices reaches 50% when using paralleling. This success is made up, which used my diagonalization, can be downloaded here: fmy2ueaad
As these improvements are included in the code of Intel MKL package, it is appropriate to give the information about the necessary changes in LAPACK (CLAPACK) code, which is the basis of Intel MKL package.
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