Press n or j to go to the next uncovered block, b, p or k for the previous block.
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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 base = require( './base.js' );
// MAIN //
/**
* Computes the singular values of a real `N-by-N` bi-diagonal matrix with diagonal `D` and off-diagonal `E`.
*
* ## Notes
*
* - `D` should have `N` indexed elements. On entry, `D` contains the diagonal elements of the bi-diagonal matrix whose SVD is desired. On normal exit, `D` contains the singular values in decreasing order.
*
* - `E` should have `N` indexed elements. On entry, elements E(1:N-1) contain the off-diagonal elements of the bi-diagonal matrix whose SVD is desired. On exit, E is overwritten.
*
* - The function returns a status code:
*
* - `= 0`: successful exit.
*
* - `< 0`: if `INFO = -i`, the `i`-th argument had an illegal value.
*
* - `> 0`: the algorithm failed:
* - `= 1`, a split was marked by a positive value in `E`.
* - `= 2`, current block of `Z` not diagonalized after `100*N` iterations (in inner while loop). On exit, `D` and `E` represent a matrix with the same singular values which the calling subroutine could use to finish the computation, or even feed back into `DLASQ1`
* - `= 3`, termination criterion of outer while loop not met (program created more than `N` unreduced blocks)
*
* @param {integer} N - number of rows/columns in the matrix
* @param {Float64Array} D - the array with diagonal elements of the bi-diagonal matrix whose SVD is desired
* @param {Float64Array} E - the array with off-diagonal elements of the bi-diagonal matrix whose SVD is desired
* @param {Float64Array} WORK - workspace array (length >= 4*N)
* @returns {integer} status code
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var D = new Float64Array( [ 100, 50, 25 ] );
* var E = new Float64Array( [ 90, 40, 0 ] );
* var WORK = new Float64Array( 16 );
*
* var info = dlasq1( 3, D, E, WORK );
* // D => <Float64Array>[ ~139.377, ~56.064, ~15.997 ]
* // E => <Float64Array>[ 90, 40, 0 ]
* // WORK => <Float64Array>[ ~1.939e292, ~3.137e291, ~2.554e290, ~1.575e286, ~3.137e291, ~2.881e291, ~2.278e292, ~2.278e292, 7.0, ~2.667, 0.0, ~2.881e291, 0, 0, 0, 0 ]
* // info => 0
*/
function dlasq1( N, D, E, WORK ) { // eslint-disable-line stdlib/jsdoc-doctest-decimal-point
return base( N, D, 1, 0, E, 1, 0, WORK, 1, 0 );
}
// EXPORTS //
module.exports = dlasq1;
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