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* @license Apache-2.0
*
* Copyright (c) 2024 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 isRowMajor = require( '@stdlib/ndarray/base/assert/is-row-major-string' );
var isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major-string' );
// MAIN //
/**
* Performs the symmetric rank 1 operation `A = α*x*x^T + A` where `α` is a scalar, `x` is an `N` element vector, and `A` is an `N` by `N` symmetric matrix supplied in packed form.
*
* @private
* @param {string} order - storage layout
* @param {string} uplo - specifies whether the upper or lower triangular part of the symmetric matrix `A` is supplied
* @param {NonNegativeInteger} N - number of elements along each dimension of `A`
* @param {number} alpha - scalar
* @param {Float64Array} x - input vector
* @param {integer} strideX - `x` stride length
* @param {NonNegativeInteger} offsetX - starting index for `x`
* @param {Float64Array} AP - packed form of a symmetric matrix `A`
* @param {integer} strideAP - `AP` stride length
* @param {NonNegativeInteger} offsetAP - starting index for `AP`
* @returns {Float64Array} `A`
*
* @example
* var Float64Array = require( '@stdlib/array/float64' );
*
* var AP = new Float64Array( [ 1.0, 2.0, 3.0, 1.0, 2.0, 1.0 ] ); // => [ [ 1.0, 2.0, 3.0 ], [ 0.0, 1.0, 2.0 ], [ 0.0, 0.0, 1.0 ] ]
* var x = new Float64Array( [ 1.0, 2.0, 3.0 ] );
*
* dspr( 'row-major', 'upper', 3, 1.0, x, 1, 0, AP, 1, 0 );
* // AP => <Float64Array>[ 2.0, 4.0, 6.0, 5.0, 8.0, 10.0 ]
*/
function dspr( order, uplo, N, alpha, x, strideX, offsetX, AP, strideAP, offsetAP ) { // eslint-disable-line max-len
var tmp;
var ix0;
var ix1;
var iap;
var i0;
var i1;
var kk;
var ox;
ox = offsetX;
kk = offsetAP;
if (
( isColumnMajor( order ) && uplo === 'upper' ) ||
( isRowMajor( order ) && uplo === 'lower' )
) {
ix1 = ox;
for ( i1 = 0; i1 < N; i1++ ) {
if ( x[ ix1 ] !== 0.0 ) {
tmp = alpha * x[ ix1 ];
ix0 = ox;
iap = kk;
for ( i0 = 0; i0 <= i1; i0++ ) {
AP[ iap ] += x[ ix0 ] * tmp;
ix0 += strideX;
iap += strideAP;
}
}
ix1 += strideX;
kk += ( i1 + 1 ) * strideAP;
}
return AP;
}
// ( order === 'column-major' && uplo === 'lower' ) || ( order === 'row-major' && uplo === 'upper' )
ix1 = ox;
for ( i1 = 0; i1 < N; i1++ ) {
if ( x[ ix1 ] !== 0.0 ) {
tmp = alpha * x[ ix1 ];
ix0 = ix1;
iap = kk;
for ( i0 = 0; i0 < N - i1; i0++ ) {
AP[ iap ] += x[ ix0 ] * tmp;
ix0 += strideX;
iap += strideAP;
}
}
ix1 += strideX;
kk += ( N - i1 ) * strideAP;
}
return AP;
}
// EXPORTS //
module.exports = dspr;
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