lamrg.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_LAMRG_HH
#define TLAPACK_LAMRG_HH
 
#include "tlapack/base/utils.hpp"
 
namespace tlapack {
 
template <class idx_t, class a_t, class idx1_t>
void lamrg(idx_t n1, idx_t n2, a_t& a, int dtrd1, int dtrd2, idx1_t& index)
{
    idx_t n1sv = n1;
    idx_t n2sv = n2;
    idx_t ind1;
    idx_t ind2;
 
    if (dtrd1 > 0) {
        ind1 = 0;
    }
    else {
        ind1 = n1 - 1;
    }
 
    if (dtrd2 > 0) {
        ind2 = n1;
    }
    else {
        ind2 = n1 + n2 - 1;
    }
 
    idx_t i = 0;
 
    while (n1sv > 0 && n2sv > 0) {
        if (a[ind1] <= a[ind2]) {
            index[i] = ind1;
            i = i + 1;
            ind1 = ind1 + dtrd1;
            n1sv = n1sv - 1;
        }
        else {
            index[i] = ind2;
            i = i + 1;
            ind2 = ind2 + dtrd2;
            n2sv = n2sv - 1;
        }
    }
 
    if (n1sv == 0) {
        for (idx_t j = 0; j < n2sv; j++) {
            index[i] = ind2;
            i = i + 1;
            ind2 = ind2 + dtrd2;
        }
    }
    else {
        for (idx_t j = 0; j < n1sv; j++) {
            index[i] = ind1;
            i = i + 1;
            ind1 = ind1 + dtrd1;
        }
    }
 
    return;
}
}  // namespace tlapack
 
#endif  // TLAPACK_LAMRG_HH