potrs.hpp

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//
// Copyright (c) 2025, University of Colorado Denver. All rights reserved.
//
// This file is part of <T>LAPACK.
// <T>LAPACK is free software: you can redistribute it and/or modify it under
// the terms of the BSD 3-Clause license. See the accompanying LICENSE file.
 
#ifndef TLAPACK_POTRS_HH
#define TLAPACK_POTRS_HH
 
#include "tlapack/base/utils.hpp"
#include "tlapack/blas/trsm.hpp"
 
namespace tlapack {
 
template <TLAPACK_UPLO uplo_t,
          TLAPACK_MATRIX matrixA_t,
          TLAPACK_MATRIX matrixB_t>
int potrs(uplo_t uplo, const matrixA_t& A, matrixB_t& B)
{
    using T = type_t<matrixB_t>;
    using real_t = real_type<T>;
 
    // Constants
    const real_t one(1);
 
    // Check arguments
    tlapack_check_false(uplo != Uplo::Lower && uplo != Uplo::Upper);
    tlapack_check_false(nrows(A) != ncols(A));
    tlapack_check_false(nrows(B) != ncols(A));
 
    if (uplo == Uplo::Upper) {
        // Solve A*X = B where A = U**H *U.
        trsm(LEFT_SIDE, UPPER_TRIANGLE, CONJ_TRANS, NON_UNIT_DIAG, one, A, B);
        trsm(LEFT_SIDE, UPPER_TRIANGLE, NO_TRANS, NON_UNIT_DIAG, one, A, B);
    }
    else {
        // Solve A*X = B where A = L*L**H.
        trsm(LEFT_SIDE, LOWER_TRIANGLE, NO_TRANS, NON_UNIT_DIAG, one, A, B);
        trsm(LEFT_SIDE, LOWER_TRIANGLE, CONJ_TRANS, NON_UNIT_DIAG, one, A, B);
    }
    return 0;
}
 
}  // namespace tlapack
 
#endif  // TLAPACK_POTRS_HH