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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 isRowMajor = require( '@stdlib/ndarray/base/assert/is-row-major' );
var sfill = require( '@stdlib/blas/ext/base/sfill' ).ndarray;
var sscal = require( '@stdlib/blas/base/sscal' ).ndarray;
var f32 = require( '@stdlib/number/float64/base/to-float32' );
// MAIN //
/**
* Performs the matrix-vector operation `y = α*A*x + β*y` where `α` and `β` are scalars, `x` and `y` are `N` element vectors, and `A` is an `N` by `N` symmetric matrix.
*
* @param {string} uplo - specifies whether the upper or lower triangular part of the symmetric matrix `A` should be referenced
* @param {NonNegativeInteger} N - number of elements along each dimension of `A`
* @param {number} alpha - scalar constant
* @param {Float32Array} A - input matrix
* @param {PositiveInteger} strideA1 - stride of the first dimension of `A`
* @param {PositiveInteger} strideA2 - stride of the second dimension of `A`
* @param {NonNegativeInteger} offsetA - starting index for `A`
* @param {Float32Array} x - first input array
* @param {integer} strideX - `x` stride length
* @param {NonNegativeInteger} offsetX - starting index for `x`
* @param {number} beta - scalar constant
* @param {Float32Array} y - second input array
* @param {integer} strideY - `y` stride length
* @param {NonNegativeInteger} offsetY - starting index for `y`
* @returns {Float32Array} `y`
*
* @example
* var Float32Array = require( '@stdlib/array/float32' );
*
* var A = new Float32Array( [ 1.0, 0.0, 0.0, 0.0, 2.0, 0.0, 0.0, 0.0, 3.0 ] );
* var x = new Float32Array( [ 1.0, 1.0, 1.0 ] );
* var y = new Float32Array( [ 0.0, 0.0, 0.0 ] );
*
* ssymv( 'lower', 3, 1.0, A, 3, 1, 0, x, 1, 0, 0.0, y, 1, 0 );
* // y => <Float32Array>[ 1.0, 2.0, 3.0 ]
*/
function ssymv( uplo, N, alpha, A, strideA1, strideA2, offsetA, x, strideX, offsetX, beta, y, strideY, offsetY ) { // eslint-disable-line max-params, max-len
var isrm;
var tmp1;
var tmp2;
var ix0;
var iy0;
var ix1;
var iy1;
var sa0;
var sa1;
var i1;
var i0;
var oa;
// Note on variable naming convention: sa#, ix#, i# where # corresponds to the loop number, with `0` being the innermost loop...
isrm = isRowMajor( [ strideA1, strideA2 ] );
if ( isrm ) {
// For row-major matrices, the last dimension has the fastest changing index...
sa0 = strideA2; // stride for innermost loop
sa1 = strideA1; // stride for outermost loop
} else { // isColMajor
// For column-major matrices, the first dimension has the fastest changing index...
sa0 = strideA1; // stride for innermost loop
sa1 = strideA2; // stride for outermost loop
}
// y = beta*y
if ( beta !== 1.0 ) {
if ( beta === 0.0 ) {
sfill( N, 0.0, y, strideY, offsetY );
} else {
sscal( N, beta, y, strideY, offsetY );
}
}
if ( alpha === 0.0 ) {
return y;
}
// Form: y = α*A*x + y
if (
( !isrm && uplo === 'upper' ) ||
( isrm && uplo === 'lower' )
) {
ix1 = offsetX;
iy1 = offsetY;
for ( i1 = 0; i1 < N; i1++ ) {
tmp1 = f32( alpha * x[ ix1 ] );
tmp2 = 0.0;
ix0 = offsetX;
iy0 = offsetY;
oa = offsetA + ( sa1 * i1 );
for ( i0 = 0; i0 < i1; i0++ ) {
y[ iy0 ] += f32( tmp1 * A[ oa + ( sa0 *i0 ) ] );
tmp2 = f32( tmp2 + f32( A[ oa + ( sa0 * i0 ) ] * x[ ix0 ] ) );
ix0 += strideX;
iy0 += strideY;
}
y[ iy1 ] += f32( f32( tmp1 * A[ oa+( sa0 * i1 ) ] ) + f32( alpha * tmp2 ) ); // eslint-disable-line max-len
ix1 += strideX;
iy1 += strideY;
}
return y;
}
// ( !isrm && uplo === 'lower' ) || ( isrm && uplo === 'upper' )
ix1 = offsetX;
iy1 = offsetY;
for ( i1 = 0; i1 < N; i1++ ) {
tmp1 = f32( alpha * x[ ix1 ] );
tmp2 = 0.0;
oa = offsetA + ( sa1 * i1 );
y[ iy1 ] += f32( tmp1 * A[ oa + ( sa0 * i1 ) ] );
ix0 = ix1;
iy0 = iy1;
for ( i0 = i1+1; i0 < N; i0++ ) {
ix0 += strideX;
iy0 += strideY;
y[ iy0 ] += f32( tmp1 * A[ oa + ( sa0 * i0 ) ] );
tmp2 = f32( tmp2 + f32( A[ oa + ( sa0 * i0 ) ] * x[ ix0 ] ) );
}
y[ iy1 ] += f32( alpha * tmp2 );
ix1 += strideX;
iy1 += strideY;
}
return y;
}
// EXPORTS //
module.exports = ssymv;
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