These are chat archives for elemental/chat

20th
Sep 2018
Adam Baskerville
@AmusingYeti_gitlab
Sep 20 2018 09:00

This is most likely a very simple question for the experts here, but I am new to using non-standard data types in C++. Part of my code produces numbers which are defined using the mpreal data type from MPFR (this cannot be changed unfortunately). I would like to redefine these as DoubleDouble from the QD library in order to build a matrix for use in the Elemental library. I cannot seem to figure out how to do this.

Another question I have is about the performance of Elemental at higher than double precision? Obviously the performance will take a big hit but I moved to Elemental from the Eigen library as Eigen does not play well with custom types (mpreal) as re-allocations for these types reduce the speed by a factor of 100+. Has anyone had experience using Elemental (specifically generalized eigenvalue calculation) at higher precision (DoubleDouble, QuadDouble etc...)

Walter Landry
@wlandry
Sep 20 2018 17:33
I am using Elemental with very high precision (~1000 bits). MPFR is about a factor of two slower than GMP, so I ended up modifying Elemental to use GMP. It is much, much slower than IEEE double's. My guess is a factor of 100?