dev_fdaPDE/Kronecker_Product.h at master · simonepanzeri/dev_fdaPDE · GitHub

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//
// Created by simonepanzeri on 25/11/2021.
//

#ifndef DEV_FDAPDE_KRONECKER_PRODUCT_H
#define DEV_FDAPDE_KRONECKER_PRODUCT_H

#include "FdaPDE.h"

//DENSE
/*
  SpMat kroneckerProduct(const SpMat& A, const SpMat& B)
{
	UInt Nr = A.rows();
	UInt Nc = A.cols();
	UInt Mr = B.rows();
	UInt Mc = B.cols();

	MatrixXr AB_dense(Nr*Mr, Nc*Mc);
	MatrixXr A_dense = Eigen::MatrixXd(A);

	for (UInt i = 0; i < Nr; ++i)
		for (UInt j = 0; j < Nc; ++j)
			AB_dense.block(i*Mr, j*Mc, Mr, Mc) =  A_dense.coeffRef(i,j)*B;

	SpMat AB = AB_dense.sparseView();

	AB.makeCompressed();

	return(AB);
}
*/

// SPARSE
/*
SpMat kroneckerProduct(const SpMat& A, const SpMat& B)
{
		UInt Nr = A.rows();
		UInt Nc = A.cols();
		UInt Mr = B.rows();
		UInt Mc = B.cols();

		SpMat AB(Nr*Mr, Nc*Mc);
		Real a;

		for (UInt i = 0; i < Nr; ++i) {
				for (UInt j = 0; j < Nc; ++j) {
						a = A.coeff(i,j);

						if(a != 0) {
								for (UInt k = 0; k < Mr; ++k)
								for (UInt l = 0; l < Mc; ++l) AB.insert(Mr*i+k, Mc*j+l) = a*B.coeff(k,l);
						}
				}
		}
		return(AB);
}
*/

SpMat kroneckerProduct(const SpMat& A, const SpMat& B) {
    UInt Ar = A.rows();
    UInt Ac = A.cols();
    UInt Br = B.rows();
    UInt Bc = B.cols();

    const Real *Avalues = A.valuePtr();
    const UInt *Ainner  = A.innerIndexPtr();
    const UInt *Aouter  = A.outerIndexPtr();
    UInt Anz            = A.nonZeros();

    const Real *Bvalues = B.valuePtr();
    const UInt *Binner  = B.innerIndexPtr();
    const UInt *Bouter  = B.outerIndexPtr();
    UInt Bnz            = B.nonZeros();

    UInt ABr  = Ar * Br;
    UInt ABc  = Ac * Bc;
    UInt ABnz = Anz * Bnz;

    //Real *ABvalues = new Real[ABnz];
    //UInt *ABinner  = new UInt[ABnz];
    //UInt *ABouter  = new UInt[ABc+1];
    std::vector<Real> ABvalues(ABnz);
    std::vector<UInt> ABinner(ABnz);
    std::vector<UInt> ABouter(ABc+1);

    ABouter[0] = 0.0;
    UInt Acurrent = Aouter[0];
    UInt ij = 0;
    UInt iijj = 0;
    for (UInt i = 1; i <= Ac; i++) {
        UInt Bcurrent = Bouter[0];
        for (UInt j = 1; j <= Bc; j++) {
            ij++;
            ABouter[ij] = ABouter[ij-1] + (Aouter[i]-Aouter[i-1]) * (Bouter[j]-Bouter[j-1]);
            for (UInt ii = Acurrent; ii < Aouter[i]; ii++) {
                for (UInt jj = Bcurrent; jj < Bouter[j]; jj++) {
                    ABinner[iijj]  = Ainner[ii] * Br + Binner[jj];
                    ABvalues[iijj] = Avalues[ii] * Bvalues[jj];
                    iijj++;
                }
            }
            Bcurrent = Bouter[j];
        }
        Acurrent = Aouter[i];
    }

    Eigen::MappedSparseMatrix<Real, Eigen::ColMajor, UInt> ABM(ABr, ABc, ABnz, ABouter.data(), ABinner.data(), ABvalues.data());
    SpMat AB(ABM);

//	delete[] ABvalues;
//	delete[] ABinner;
//	delete[] ABouter;

    return(AB);
}


MatrixXr kroneckerProduct_Matrix (const MatrixXr& A, const MatrixXr& B)
{
    MatrixXr C;
    C.resize(A.rows()*B.rows(),A.cols()*B.cols());
    UInt r = 0, c = 0;
    for (UInt i = 0; i < A.rows(); i++) {
        for (UInt k = 0; k < B.rows(); k++) {
            for (UInt j = 0; j < A.cols(); j++) {
                for (UInt l = 0; l < B.cols(); l++){
                    C(r,c) = A(i,j) * B(k,l); c++;
                }
            }
            c=0; r++;
        }
    }
    return C;
}

#endif //DEV_FDAPDE_KRONECKER_PRODUCT_H