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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 isRowMajor = require( '@stdlib/ndarray/base/assert/is-row-major-string' );
var isColumnMajor = require( '@stdlib/ndarray/base/assert/is-column-major-string' );
// MAIN //
/**
* Performs the matrix-vector operation `y = alpha*A*x + beta*y` where `alpha` and `beta` are scalars, `x` and `y` are `N` element vectors, 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 constant
* @param {Object} AP - packed matrix object
* @param {Collection} AP.data - packed matrix data
* @param {Array<Function>} AP.accessors - array element accessors
* @param {NonNegativeInteger} offsetAP - starting index for `AP`
* @param {Object} x - first input vector object
* @param {Collection} x.data - first input vector data
* @param {Array<Function>} x.accessors - array element accessors
* @param {integer} strideX - `x` stride length
* @param {NonNegativeInteger} offsetX - starting index for `x`
* @param {number} beta - scalar constant
* @param {Object} y - second input vector object
* @param {Collection} y.data - second input vector data
* @param {Array<Function>} y.accessors - array element accessors
* @param {integer} strideY - `y` stride length
* @param {NonNegativeInteger} offsetY - starting index for `y`
* @returns {Object} second input vector object
*/
function gspmv( order, uplo, N, alpha, AP, offsetAP, x, strideX, offsetX, beta, y, strideY, offsetY ) { // eslint-disable-line max-params, max-len
var APbuf;
var getAP;
var temp1;
var temp2;
var setY;
var getY;
var getX;
var xbuf;
var ybuf;
var ix;
var iy;
var jx;
var jy;
var kk;
var j;
var k;
// Cache references to array data:
xbuf = x.data;
ybuf = y.data;
APbuf = AP.data;
// Cache references to element accessors:
getX = x.accessors[ 0 ];
getY = y.accessors[ 0 ];
setY = y.accessors[ 1 ];
getAP = AP.accessors[ 0 ];
// Form: y = beta*y
if ( beta !== 1.0 ) {
iy = offsetY;
if ( beta === 0.0 ) {
for ( k = 0; k < N; k++ ) {
setY( ybuf, iy, 0.0 );
iy += strideY;
}
} else {
for ( k = 0; k < N; k++ ) {
setY( ybuf, iy, beta * getY( ybuf, iy ) );
iy += strideY;
}
}
}
if ( alpha === 0.0 ) {
return y;
}
// Form: y = alpha*A*x + y
kk = offsetAP;
if (
( isRowMajor( order ) && uplo === 'upper' ) ||
( isColumnMajor( order ) && uplo === 'lower' )
) {
jx = offsetX;
jy = offsetY;
for ( j = 0; j < N; j++ ) {
temp1 = alpha * getX( xbuf, jx );
temp2 = 0.0;
setY( ybuf, jy, getY( ybuf, jy ) + ( temp1 * getAP( APbuf, kk ) ) );
ix = jx;
iy = jy;
for ( k = kk+1; k < kk+N-j; k++ ) {
ix += strideX;
iy += strideY;
setY( ybuf, iy, getY( ybuf, iy ) + ( temp1 * getAP( APbuf, k ) ) );
temp2 += getAP( APbuf, k ) * getX( xbuf, ix );
}
setY( ybuf, jy, getY( ybuf, jy ) + ( alpha * temp2 ) );
jx += strideX;
jy += strideY;
kk += N - j;
}
return y;
}
// ( isRowMajor( order ) && uplo === 'lower' ) || ( isColumnMajor( order ) && uplo === 'upper' )
jx = offsetX;
jy = offsetY;
for ( j = 0; j < N; j++ ) {
temp1 = alpha * getX( xbuf, jx );
temp2 = 0.0;
ix = offsetX;
iy = offsetY;
for ( k = kk; k < kk+j; k++ ) {
setY( ybuf, iy, getY( ybuf, iy ) + ( temp1 * getAP( APbuf, k ) ) );
temp2 += getAP( APbuf, k ) * getX( xbuf, ix );
ix += strideX;
iy += strideY;
}
setY( ybuf, jy, getY( ybuf, jy ) + ( temp1 * getAP( APbuf, kk+j ) ) + ( alpha * temp2 ) ); // eslint-disable-line max-len
jx += strideX;
jy += strideY;
kk += j + 1;
}
return y;
}
// EXPORTS //
module.exports = gspmv;
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