Re: [uBlas] [Tensor] multiprecision and FFT?

From: Cem Bassoy (cem.bassoy_at_[hidden])
Date: 2021-01-07 11:43:47

Am Mi., 6. Jan. 2021 um 23:19 Uhr schrieb Janek Kozicki via Boost <
boost_at_[hidden]>:

> Cem Bassoy via Boost said:     (by the date of Wed, 6 Jan 2021 10:32:15
> +0100)
>
> > Please consider to use and contribute to *Boost.uBlas*
>
>
> Hi,
>
> Does it work with boost::multiprecision types? In particular I am
> interested in types listed here:
>
> http://yade-dem.org/doc/HighPrecisionReal.html
>
>
It does work with *boost::multiprecision*:
Have a look @ https://godbolt.org/z/cMKc9T

>
> Does it support FFT ?

You can get the pointer (like for vector) to the underlying contiguous
memory (you do not own the memory):

using format_t  = boost::numeric::ublas::column_major;

using tensor_t = boost::numeric::ublas::tensor<float,format_t>;
auto A = tensor_t(shape{3,4,2},2);auto ap = A.data();

You can also use the standard c++ library for convenience:

std::for_each(A.begin(), A.end(), [](auto& a){ ++a; });

If you do not want to use the Einstein-notation, you can as well use either
the prod function:

// C3(i,l1,l2) = A(i,j,k)*T1(l1,j)*T2(l2,k);

q = 3u;

tensor_t C3 = prod(prod(A,matrix_t(m+1,n[q-2],1),q-1),matrix_t(m+2,n[q-1],1),q);

"prod" uses internally a C-like interface which will not allocate memory
at all.

ttm(m, p,

    c.data(), c.extents().data(), c.strides().data(),

    a.data(), a.extents().data(), a.strides().data(),

    bb, nb.data(), wb.data());

Cheers,
Cem

> In particular I am interested in replacing my
> very crude NDimTable class with your code:
>
>
> https://gitlab.com/cosurgi/trunk/-/blob/addQuantumMechanics_FixEnum_FixRebase1/lib/base/NDimTable.hpp
>
> I am about to start refactoring this part of the code, when I noticed your
> post.
>
> best regards
> Janek
>
>
> --
> Janek Kozicki, PhD. DSc. Arch. Assoc. Prof.
> Gdańsk University of Technology
> Faculty of Applied Physics and Mathematics
> Department of Theoretical Physics and Quantum Information
> --
> http://yade-dem.org/
> http://pg.edu.pl/jkozicki (click English flag on top right)
>
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