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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.
*/
'use strict';
// MODULES //
var idamax = require( '@stdlib/blas/base/idamax' ).ndarray;
var dscal = require( '@stdlib/blas/base/dscal' ).ndarray;
var dswap = require( '@stdlib/blas/base/dswap' ).ndarray;
var dger = require( '@stdlib/blas/base/dger' ).ndarray;
// MAIN //
/**
* Computes an `LU` factorization of a real general matrix `A` using elimination with partial pivoting and row interchanges.
*
* @private
*
* ## Notes
*
* - The factorization has the form `A = P * L * U`, where `P` is a permutation matrix, `L` is lower triangular or trapezoidal with unit diagonal elements, and `U` is upper triangular or trapezoidal.
* - `A` is overwritten in-place. The strictly lower triangular part contains the multipliers defining `L`, and the upper triangular part contains `U`. The unit diagonal of `L` is not stored.
* - `IPIV` contains zero-based pivot indices. For each `i` in `0 <= i < min(M,N)`, row `i` is interchanged with row `IPIV(i)`.
* - If the returned status code is greater than zero, `U(k,k)` is exactly zero for `k` equal to the status code. The factorization has been completed, but `U` is singular.
* @param {NonNegativeInteger} M - number of rows in `A`
* @param {NonNegativeInteger} N - number of columns in `A`
* @param {Float64Array} A - input matrix
* @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 {Int32Array} IPIV - vector of pivot indices
* @param {integer} strideIPIV - stride length for `IPIV`
* @param {NonNegativeInteger} offsetIPIV - starting index for `IPIV`
* @returns {integer} status code
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var Int32Array = require( '@stdlib/array/int32' );
*
* var A = new Float64Array( [ 1.0, 3.0, 2.0, 4.0 ] );
* var IPIV = new Int32Array( 2 );
*
* dgetrf( 2, 2, A, 1, 2, 0, IPIV, 1, 0 );
* // A => <Float64Array>[ 3, 0.333..., 4, 0.666... ]
* // IPIV => <Int32Array>[ 1, 1 ]
*/
function dgetrf( M, N, A, strideA1, strideA2, offsetA, IPIV, strideIPIV, offsetIPIV ) { // eslint-disable-line max-params, max-len
var mn;
var info;
var ia;
var jp;
var j;
mn = M < N ? M : N;
info = 0;
for ( j = 0; j < mn; j++ ) {
ia = offsetA + ( j * strideA2 ) + ( j * strideA1 );
jp = j + idamax( M-j, A, strideA1, ia );
IPIV[ offsetIPIV + ( j * strideIPIV ) ] = jp;
if ( A[ offsetA + ( jp * strideA1 ) + ( j * strideA2 ) ] !== 0.0 ) {
if ( jp !== j ) {
dswap( N, A, strideA2, offsetA+(j*strideA1), A, strideA2, offsetA+(jp*strideA1) ); // eslint-disable-line max-len
}
if ( j < M-1 ) {
dscal( M-j-1, 1.0/A[ ia ], A, strideA1, ia+strideA1 );
}
}
if ( A[ ia ] === 0.0 ) {
if ( info === 0 ) {
info = j+1;
}
}
if ( A[ ia ] !== 0.0 && j < mn-1 ) {
dger( M-j-1, N-j-1, -1.0, A, strideA1, ia+strideA1, A, strideA2, ia+strideA2, A, strideA1, strideA2, ia+strideA1+strideA2 );
}
}
return info;
}
// EXPORTS //
module.exports = dgetrf;
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