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* @license Apache-2.0
*
* Copyright (c) 2026 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* eslint-disable max-len, max-params */
'use strict';
// MODULES //
var dlarf1f = require( '@stdlib/lapack/base/dlarf1f' ).ndarray;
// FUNCTIONS //
/**
* Tests whether an operation should be applied to the left side.
*
* @private
* @param {string} side - operation side
* @returns {boolean} boolean indicating if an operation should be applied to the left side
*/
function isLeftSide( side ) {
return side === 'left';
}
// MAIN //
/**
* Multiply a general matrix by the orthogonal matrix from a LQ factorization determined by `DGELQF`.
*
* ## Notes
*
* - `Q` is a real orthogonal matrix defined as the product of k elementary reflectors, Q = H(k) . . . H(2) H(1) as returned by `DGELQF`.
*
* - `Q` is of order `M` if SIDE = 'left' and of order `N` if SIDE = 'R'.
*
* - `DORML2` overwrites the general real `M` by `N` matrix `C` with,
*
* - `Q * C` if SIDE = 'left' and TRANS = 'no-transpose', or
* - `Q^T* C` if SIDE = 'left' and TRANS = 'transpose', or
* - `C * Q` if SIDE = 'right' and TRANS = 'no-transpose', or
* - `C * Q**T` if SIDE = 'right' and TRANS = 'transpose'.
*
* @private
* @param {string} side - specifies the side of multiplication with `C`
* @param {string} trans - `'no-transpose'` for `Q`, `'transpose'` for `Q^T`
* @param {NonNegativeInteger} M - number of rows of `C`
* @param {NonNegativeInteger} N - number of columns of `C`
* @param {NonNegativeInteger} K - number of elementary reflectors
* @param {Float64Array} A - reflector vectors from `DGELQ2`
* @param {integer} strideA1 - stride of the first dimension of A
* @param {integer} strideA2 - stride of the second dimension of A
* @param {NonNegativeInteger} offsetA - starting index for A
* @param {Float64Array} TAU - scalar factors of reflectors
* @param {integer} strideTAU - stride for TAU
* @param {NonNegativeInteger} offsetTAU - starting index for TAU
* @param {Float64Array} C - input/output matrix
* @param {integer} strideC1 - stride of the first dimension of `C`
* @param {integer} strideC2 - stride of the second dimension of `C`
* @param {NonNegativeInteger} offsetC - starting index for `C`
* @param {Float64Array} WORK - workspace array
* @param {integer} strideWORK - stride for `WORK`
* @param {NonNegativeInteger} offsetWORK - starting index for `WORK`
* @returns {integer} status code (0 if successful)
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var A = new Float64Array( [ 1, 0 ] );
* var TAU = new Float64Array( [ 2 ] );
* var C = new Float64Array( [ 1, 3, 5, 2, 4, 6 ] );
* var WORK = new Float64Array( 3 );
*
* var info = dorml2( 'left', 'no-transpose', 2, 3, 1, A, 2, 1, 0, TAU, 1, 0, C, 3, 1, 0, WORK, 1, 0 );
* // returns 0
* // C => <Float64Array>[ -1, -3, -5, 2, 4, 6 ]
* // WORK => <Float64Array>[ 1, 3, 5 ]
*/
function dorml2( side, trans, M, N, K, A, strideA1, strideA2, offsetA, TAU, strideTAU, offsetTAU, C, strideC1, strideC2, offsetC, WORK, strideWORK, offsetWORK ) {
var isTrans;
var isLeft;
var idx0;
var idx1;
var idx2;
var mi;
var ni;
var ic;
var jc;
var i1;
var i2;
var i3;
var i;
isLeft = isLeftSide( side );
isTrans = ( trans === 'transpose' );
// Quick return if possible
if ( M === 0 || N === 0 || K === 0 ) {
return 0;
}
if ( ( isLeft && !isTrans ) || ( !isLeft && isTrans ) ) {
i1 = 0;
i2 = K - 1;
i3 = 1;
} else {
i1 = K - 1;
i2 = 0;
i3 = -1;
}
if ( isLeft ) {
ni = N;
jc = 0;
idx0 = offsetA + ( i1*strideA1 ) + ( i1*strideA2 );
idx1 = offsetTAU + ( i1*strideTAU );
idx2 = offsetC + ( i1*strideC1 ) + ( jc*strideC2 );
for ( i = i1; ( i3 > 0 ) ? ( i <= i2 ) : ( i >= i2 ); i += i3 ) {
// Apply H(i) to C(i:M-1, 0:N-1)
mi = M - i;
ic = i;
// Apply H(i): the reflector vector is row i of A starting at column i,
dlarf1f( side, mi, ni, A, strideA2, idx0, TAU[ idx1 ], C, strideC1, strideC2, idx2, WORK, strideWORK, offsetWORK );
idx0 += i3*( strideA1 + strideA2 );
idx1 += i3*strideTAU;
idx2 += i3*strideC1;
}
} else {
mi = M;
ic = 0;
idx0 = offsetA + ( i1*strideA1 ) + ( i1*strideA2 );
idx1 = offsetTAU + ( i1*strideTAU );
idx2 = offsetC + ( ic*strideC1 ) + ( i1*strideC2 );
for ( i = i1; ( i3 > 0 ) ? ( i <= i2 ) : ( i >= i2 ); i += i3 ) {
// Apply H(i) to C(0:M-1, i:N-1)
ni = N - i;
jc = i;
// Apply H(i): the reflector vector is row i of A starting at column i,
dlarf1f( side, mi, ni, A, strideA2, idx0, TAU[ idx1 ], C, strideC1, strideC2, idx2, WORK, strideWORK, offsetWORK );
idx0 += i3*( strideA1 + strideA2 );
idx1 += i3*strideTAU;
idx2 += i3*strideC2;
}
}
return 0;
}
// EXPORTS //
module.exports = dorml2;
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