dynare/mex/sources/kronecker/A_times_B_kronecker_C.f08

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! This MEX file computes A·(B⊗C) or A·(B⊗B) without explicitly building B⊗C or
! B⊗B, so that one can consider large matrices B and/or C.
! Copyright © 2007-2023 Dynare Team
!
! This file is part of Dynare.
!
! Dynare is free software: you can redistribute it and/or modify
! it under the terms of the GNU General Public License as published by
! the Free Software Foundation, either version 3 of the License, or
! (at your option) any later version.
!
! Dynare is distributed in the hope that it will be useful,
! but WITHOUT ANY WARRANTY; without even the implied warranty of
! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
! GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License
! along with Dynare. If not, see <https://www.gnu.org/licenses/>.
subroutine mexFunction(nlhs, plhs, nrhs, prhs) bind(c, name='mexFunction')
use iso_fortran_env
use iso_c_binding
use matlab_mex
use blas
implicit none (type, external)
type(c_ptr), dimension(*), intent(in), target :: prhs
type(c_ptr), dimension(*), intent(out) :: plhs
integer(c_int), intent(in), value :: nlhs, nrhs
integer(c_size_t) :: mA, nA, mB, nB, mC, nC
real(real64), dimension(:, :), pointer, contiguous :: A, B, C, D
if (nrhs > 3 .or. nrhs < 2 .or. nlhs /= 1) then
call mexErrMsgTxt("A_times_B_kronecker_C takes 2 or 3 input arguments and provides 1 output argument")
end if
if (.not. mxIsDouble(prhs(1)) .or. mxIsComplex(prhs(1)) .or. mxIsSparse(prhs(1)) &
.or. .not. mxIsDouble(prhs(2)) .or. mxIsComplex(prhs(2)) .or. mxIsSparse(prhs(2))) then
call mexErrMsgTxt("A_times_B_kronecker_C: first two arguments should be real dense matrices")
end if
mA = mxGetM(prhs(1))
nA = mxGetN(prhs(1))
mB = mxGetM(prhs(2))
nB = mxGetN(prhs(2))
A(1:mA,1:nA) => mxGetPr(prhs(1))
B(1:mB,1:nB) => mxGetPr(prhs(2))
if (nrhs == 3) then
! A·(B⊗C) is to be computed.
if (.not. mxIsDouble(prhs(3)) .or. mxIsComplex(prhs(3)) .or. mxIsSparse(prhs(3))) then
call mexErrMsgTxt("A_times_B_kronecker_C: third argument should be a real dense matrix")
end if
mC = mxGetM(prhs(3))
nC = mxGetN(prhs(3))
if (mB*mC /= nA) then
call mexErrMsgTxt("Input dimension error!")
end if
C(1:mC,1:nC) => mxGetPr(prhs(3))
plhs(1) = mxCreateDoubleMatrix(mA, nB*nC, mxREAL)
D(1:mA,1:nB*nC) => mxGetPr(plhs(1))
call full_A_times_kronecker_B_C
else
! A·(B⊗B) is to be computed.
if (mB*mB /= nA) then
call mexErrMsgTxt("Input dimension error!")
end if
plhs(1) = mxCreateDoubleMatrix(mA, nB*nB, mxREAL)
D(1:mA,1:nB*nB) => mxGetPr(plhs(1))
call full_A_times_kronecker_B_B
end if
contains
! Computes D=A·(B⊗C)
subroutine full_A_times_kronecker_B_C
integer(c_size_t) :: i, j, ka, kd
kd = 1
do j = 1,nB
ka = 1
do i = 1,mB
! D(:,kd:kd+nC) += B(i,j)·A(:,ka:ka+mC)·C
call dgemm("N", "N", int(mA, blint), int(nC, blint), int(mC, blint), B(i,j), &
A(:,ka:ka+mC), int(mA, blint), C, int(mC, blint), 1._real64, &
D(:,kd:kd+nC), int(mA, blint))
ka = ka + mC
end do
kd = kd + nC
end do
end subroutine full_A_times_kronecker_B_C
! Computes D=A·(B⊗B)
subroutine full_A_times_kronecker_B_B
integer(c_size_t) :: i, j, ka, kd
kd = 1
do j = 1,nB
ka = 1
do i = 1,mB
! D(:,kd:kd+nB) += B(i,j)·A(:,ka:ka+mB)·B
call dgemm("N", "N", int(mA, blint), int(nB, blint), int(mB, blint), B(i,j), &
A(:,ka:ka+mB), int(mA, blint), B, int(mB, blint), 1._real64, &
D(:,kd:kd+nB), int(mA, blint))
ka = ka + mB
end do
kd = kd + nB
end do
end subroutine full_A_times_kronecker_B_B
end subroutine mexFunction