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* @license Apache-2.0
*
* Copyright (c) 2025 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 format = require( '@stdlib/string/format' );
var isMatrixTriangle = require( '@stdlib/blas/base/assert/is-matrix-triangle' );
var base = require( './base.js' );
// MAIN //
/**
* Computes the row and column scaling factors intended to equilibrate a symmetric positive definite matrix `A` in packed storage and reduce it's condition number (with respect to the two-norm).
*
* ## Notes
*
* - the function returns `0` if it sucessfully exits.
* - if the function returns an integer `i` greater then zero then the `i`th diagonal element was non positive.
* - the first indexed element of `out` represents `scond` and the second indexed elements represents `amax`, if it `scond` >= 0.1 and `amax` is not close to overflow/underflow then it is not worth scaling by `S`.
* - if `amax` is too close to overflow/underflow, the matrix should be scaled.
*
* @param {string} order - storage layout
* @param {string} uplo - specifies whether upper or lower triangle of `A` is stored ( `upper` or `lower` )
* @param {NonNegativeInteger} N - number of rows/columns in `A`
* @param {Float64Array} AP - array containing the upper or lower triangle of `A` in packed form, expects `N * ( N + 1 ) / 2` indexed elements
* @param {Float64Array} S - array to store the scale factors of `A`, expects `N` indexed elements
* @param {Float64Array} out - array to store the output
* @throws {TypeError} first argument must be a valid order
* @throws {TypeError} second argument must be a valid side
* @throws {RangeError} third argument must be a nonnegative integer
* @returns {integer} status code
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var AP = new Float64Array( [ 1.0, 2.0, 3.0, 5.0, 6.0, 9.0 ] );
* var S = new Float64Array( 3 );
* var out = new Float64Array( 2 );
*
* dppequ( 'row-major', 'lower', 3, AP, S, out );
* // S => <Float64Array>[ 1, ~0.58, ~0.33 ]
* // out => <Float64Array>[ ~0.33, 9 ]
*/
function dppequ( order, uplo, N, AP, S, out ) {
if ( !isLayout( order ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a valid order. Value: `%s`.', order ) );
}
if ( !isMatrixTriangle( uplo ) ) {
throw new TypeError( format( 'invalid argument. Second argument must be a valid side. Value: `%s`.', order ) );
}
if ( N < 0 ) {
throw new RangeError( format( 'invalid argument. Third argument must be a nonnegative integer. Value: `%d`.', N ) );
}
return base( order, uplo, N, AP, 1, 0, S, 1, 0, out, 1, 0 );
}
// EXPORTS //
module.exports = dppequ;
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