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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 isLayout = require( '@stdlib/blas/base/assert/is-layout' );
var isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major-string' );
var max = require( '@stdlib/math/base/special/fast/max' );
var format = require( '@stdlib/string/format' );
var base = require( './base.js' );
// MAIN //
/**
* Solves a system of linear equations `A * X = B`, where `A` is an `N`-by-`N` tridiagonal matrix, using Gaussian elimination with partial pivoting.
*
* @param {string} order - storage layout of `B`
* @param {NonNegativeInteger} N - number of rows/columns in `A`
* @param {NonNegativeInteger} NRHS - number of right-hand sides (i.e., number of columns in `B`)
* @param {Float64Array} DL - the first sub-diagonal of `A`
* @param {Float64Array} D - the diagonal of `A`
* @param {Float64Array} DU - the first super-diagonal of `A`
* @param {Float64Array} B - input matrix
* @param {integer} LDB - stride of the first dimension of `B` (a.k.a., leading dimension of the matrix `B`)
* @throws {TypeError} first argument must be a valid order
* @throws {RangeError} second argument must be a nonnegative integer
* @throws {RangeError} third argument must be a nonnegative integer
* @throws {RangeError} eighth argument must be greater than or equal to max(1,N)
* @returns {integer} status code
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var DL = new Float64Array( [ 1.0, 1.0 ] );
* var D = new Float64Array( [ 2.0, 3.0, 1.0 ] );
* var DU = new Float64Array( [ 1.0, 1.0 ] );
* var B = new Float64Array( [ 4.0, 10.0, 5.0 ] );
*
* dgtsv( 'column-major', 3, 1, DL, D, DU, B, 3 );
* // B => <Float64Array>[ 1.0, 2.0, 3.0 ]
*/
function dgtsv( order, N, NRHS, DL, D, DU, B, LDB ) { // eslint-disable-line stdlib/jsdoc-doctest-decimal-point
var sb1;
var sb2;
var s;
if ( !isLayout( order ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a valid order. Value: `%s`.', order ) );
}
if ( N < 0 ) {
throw new RangeError( format( 'invalid argument. Second argument must be a nonnegative integer. Value: `%d`.', N ) );
}
if ( NRHS < 0 ) {
throw new RangeError( format( 'invalid argument. Third argument must be a nonnegative integer. Value: `%d`.', NRHS ) );
}
if ( isColumnMajor( order ) ) {
s = N;
} else {
s = NRHS;
}
if ( LDB < max( 1, s ) ) {
throw new RangeError( format( 'invalid argument. Eighth argument must be greater than or equal to max(1,%d). Value: `%d`.', s, LDB ) );
}
if ( isColumnMajor( order ) ) {
sb1 = 1;
sb2 = LDB;
} else { // order === 'row-major'
sb1 = LDB;
sb2 = 1;
}
return base( N, NRHS, DL, 1, 0, D, 1, 0, DU, 1, 0, B, sb1, sb2, 0 );
}
// EXPORTS //
module.exports = dgtsv;
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