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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 format = require( '@stdlib/string/format' );
var base = require( './base.js' );
// MAIN //
/**
* Computes an `LU` factorization of a matrix `T - lambda*I`, where `T` is a general real tridiagonal matrix, and `lambda` a scalar, using partial pivoting with row interchanges.
*
* ## Notes
*
* - `A` should have `N` elements and is overwritten by the diagonal elements of `U`.
* - `B` should have `N-1` elements and is overwritten by the first super-diagonal elements of `U`.
* - `C` should have `N-1` elements and is overwritten by the multipliers that define `L`.
* - `D` should have `N-2` elements and is overwritten by the second super-diagonal elements of `U`.
* - `IN` should have `N` elements and is overwritten by the pivot details and singularity info.
*
* @param {NonNegativeInteger} N - order of the matrix T
* @param {Float64Array} A - diagonal elements of T
* @param {number} lambda - scalar constant
* @param {Float64Array} B - super-diagonal elements of T
* @param {Float64Array} C - sub-diagonal elements of T
* @param {number} tol - tolerance constant
* @param {Float64Array} D - second super-diagonal elements of U
* @param {Int32Array} IN - pivot and singularity indices
* @throws {RangeError} first argument must be a nonnegative integer
* @returns {integer} status code
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
* var Int32Array = require( '@stdlib/array/int32' );
* var dlagtf = require( '@stdlib/lapack/base/dlagtf' );
*
* var A = new Float64Array( [ 2.0, 3.0, 1.0 ] );
* var B = new Float64Array( [ 1.0, 1.0 ] );
* var C = new Float64Array( [ 1.0, 1.0 ] );
* var D = new Float64Array( [ 0.0 ] );
* var IN = new Int32Array( [ 0, 0, 0 ] );
*
* dlagtf( 3, A, 0.0, B, C, 0.0, D, IN );
* // A => <Float64Array>[ 2.0, 2.5, 0.6 ]
* // B => <Float64Array>[ 1.0, 1.0 ]
* // C => <Float64Array>[ 0.5, 0.4 ]
* // D => <Float64Array>[ 0.0 ]
* // IN => <Int32Array>[ 0, 0, 0 ]
*/
function dlagtf( N, A, lambda, B, C, tol, D, IN ) { // eslint-disable-line stdlib/jsdoc-doctest-decimal-point
if ( N < 0 ) {
throw new RangeError( format( 'invalid argument. First argument must be a nonnegative integer. Value: `%d`.', N ) );
}
return base( N, A, 1, 0, lambda, B, 1, 0, C, 1, 0, tol, D, 1, 0, IN, 1, 0 );
}
// EXPORTS //
module.exports = dlagtf;
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