preconditioner_ssor.h

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#ifndef MUI_PRECONDITIONER_SSOR_H_
#define MUI_PRECONDITIONER_SSOR_H_
 
#include <math.h>
#include <limits>
 
namespace mui {
namespace linalg {
 
// Constructor
template<typename ITYPE, typename VTYPE>
symmetric_successive_over_relaxation_preconditioner<ITYPE,VTYPE>::symmetric_successive_over_relaxation_preconditioner(const sparse_matrix<ITYPE,VTYPE>& A, VTYPE omega)
 : A_(A), omega_(omega) {}
 
// Destructor
template<typename ITYPE, typename VTYPE>
symmetric_successive_over_relaxation_preconditioner<ITYPE,VTYPE>::~symmetric_successive_over_relaxation_preconditioner() {
    // Deallocate the memory for the coefficient matrix
    A_.set_zero();
    // Set the relaxation parameter to null
    omega_ = 0;
}
 
// Member function on preconditioner apply
template<typename ITYPE, typename VTYPE>
sparse_matrix<ITYPE,VTYPE> symmetric_successive_over_relaxation_preconditioner<ITYPE,VTYPE>::apply(const sparse_matrix<ITYPE,VTYPE>& x) {
    assert((x.get_cols()==1) &&
        "MUI Error [preconditioner_ssor.h]: apply only works for column vectors");
    sparse_matrix<ITYPE,VTYPE> y(x.get_rows(), x.get_cols());
    sparse_matrix<ITYPE,VTYPE> z(x.get_rows(), x.get_cols());
 
    // Forward substitution
    for (ITYPE i = 0; i < A_.get_rows(); ++i) {
        VTYPE sum = 0;
        for (ITYPE j = 0; j < A_.get_cols(); ++j) {
            if (i < j) {
                sum += A_.get_value(i,j) * y.get_value(j,0);
            } else if (i == j) {
                assert(std::abs(omega_ * A_.get_value(i,j)) >= std::numeric_limits<VTYPE>::min() &&
                  "MUI Error [preconditioner_ssor.h]: Divide by zero assert for omega_ * A_.get_value(i,j)");
                y.set_value(i, 0, ((x.get_value(i,0) - sum) / (omega_ * A_.get_value(i,j))));
            }
        }
    }
 
    // Back substitution
    for (ITYPE i = A_.get_rows() - 1; i >= 0; i--) {
        VTYPE sum = 0;
        for (ITYPE j = 0; j < A_.get_cols(); ++j) {
            if (i > j) {
                sum += A_.get_value(i,j) * z.get_value(j,0);
            } else if (i == j) {
                assert(std::abs(A_.get_value(i,j)) >= std::numeric_limits<VTYPE>::min() &&
                  "MUI Error [preconditioner_ssor.h]: Divide by zero assert for A_.get_value(i,j)");
                z.set_value(i, 0, (omega_ * (y.get_value(i,0) - sum) / A_.get_value(i,j)));
            }
        }
    }
    return z;
}
 
} // linalg
} // mui
 
#endif /* MUI_PRECONDITIONER_SSOR_H_ */