bassoy/ttm

C++ Header-Only Library for High-Performance Tensor-Matrix Multiplication

High-Performance Tensor-Matrix Multiplication Library - TLIB(TTM)

Summary

TLIB(TTM) is C++ high-performance tensor-matrix multiplication header-only library. It provides free C++ functions for parallel computing the mode-q tensor-times-matrix product of the general form

$$ \underline{\mathbf{C}} = \underline{\mathbf{A}} \bullet_q \mathbf{B} \quad :\Leftrightarrow \quad \underline{\mathbf{C}} (i_1, \dots, i_{q-1}, j, i_{q+1}, \dots, i_p) = \sum_{i_q=1}^{n_q} \underline{\mathbf{A}}({i_1, \dots, i_q, \dots, i_p}) \cdot \mathbf{B}({j,i_q}). $$

where $q$ is the contraction mode, $\underline{\mathbf{A}}$ and $\underline{\mathbf{C}}$ are tensors of order $p$ with shapes $\mathbf{n}_a= (n_1,\dots n_{q-1},n_q ,n_{q+1},\dots,n_p)$ and $\mathbf{n}_c = (n_1,\dots,n_{q-1},m,n_{q+1},\dots,n_p)$, respectively. The order $2$ tensor $\mathbf{B}$ is a matrix with shape $\mathbf{n}_b = (m,n_{q})$.

Usage & Installation

Please have a look at the wiki page for more informations about library usage, function interfaces and the parameters settings.

Key Features

Flexibility

• Contraction mode $q$, tensor order $p$, tensor extents $n$ and tensor layout $\mathbf{\pi}$ can be chosen at runtime
• Supports any linear tensor layout inlcuding the first-order and last-order storage layouts
• Offers two high-level and one C-like low-level interfaces for calling the tensor-times-matrix multiplication
• Implemented independent of a tensor data structure (can be used with std::vector and std::array)
• Currently supports float and double

Performance

• Multi-threading support with OpenMP v4.5 or higher
• Currently must be used with a BLAS implementation
• Performs in-place operations without transposing the tensor - no extra memory needed
• For large tensors reaches peak matrix-times-matrix performance

Requirements

• Requires the tensor elements to be contiguously stored in memory.
• Element types must be either float or double.

Python Example

import numpy as np
import ttmpy as tp

A = np.arange(4*3*2, dtype=np.float64).reshape(4,3,2)
B = np.arange(5*4,   dtype=np.float64).reshape(5,4)
C = tp.ttm(1,A,B)
D = np.einsum("ijk,xi->xjk", A, B)
np.all(np.equal(C,D))

C++ Example

/*main.cpp*/
#include <tlib/ttm.h>

#include <vector>
#include <numeric>
#include <iostream>


int main()
{
    using value_t    = float;
    using tensor_t   = tlib::tensor<value_t>;

    auto A = tensor_t( {4,3,2} );
    auto B = tensor_t( {5,4}   );

    std::iota(A.begin(),A.end(),1);
    std::fill(B.begin(),B.end(),1);
    
    std::cout << "A = " << A << std::endl;
    std::cout << "B = " << B << std::endl;

/*
  A =
  { 1  5  9  | 13 17 21
    2  6 10  | 14 18 22
    3  7 11  | 15 19 23
    4  8 12  | 16 20 24 };

  B =
  { 1  1  1  1  1
    1  1  1  1  1
    1  1  1  1  1
    1  1  1  1  1};
*/

    auto C = A (1)* B;

    std::cout << "C = " << C << std::endl;


/* for q=1
  C =
  { 1+..+4 5+..+8 9+..+12 | 13+..+16 17+..+20 21+..+24
      ..     ..     ..    |    ..       ..       ..
    1+..+4 5+..+8 9+..+12 | 13+..+16 17+..+20 21+..+24 };
*/
}