71 lines
1.8 KiB
JavaScript
71 lines
1.8 KiB
JavaScript
/**
|
|
* @license Apache-2.0
|
|
*
|
|
* Copyright (c) 2018 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 isSquareMatrix = require( './../../is-square-matrix' );
|
|
|
|
|
|
// MAIN //
|
|
|
|
/**
|
|
* Tests if a value is a symmetric matrix.
|
|
*
|
|
* ## Notes
|
|
*
|
|
* - The implementation must rely on manually checking that \\(M_{ij} = M_{ji}\\), and, while element access is deterministic, no way exists to prevent cache misses outside of reordering the underlying matrix elements, thus incurring a larger performance penalty than just "jumping around" in a single pass.
|
|
* - Worst case scenario: O(N^2).
|
|
*
|
|
* @param {*} v - value to test
|
|
* @returns {boolean} boolean indicating if a value is a symmetric matrix
|
|
*
|
|
* @example
|
|
* var ndarray = require( '@stdlib/ndarray/ctor' );
|
|
*
|
|
* var arr = ndarray( 'generic', [ 0, 1, 1, 2 ], [ 2, 2 ], [ 2, 1 ], 0, 'row-major' );
|
|
* var bool = isSymmetricMatrix( arr );
|
|
* // returns true
|
|
*
|
|
* bool = isSymmetricMatrix( [] );
|
|
* // returns false
|
|
*/
|
|
function isSymmetricMatrix( v ) {
|
|
var M;
|
|
var i;
|
|
var j;
|
|
if ( !isSquareMatrix( v ) ) {
|
|
return false;
|
|
}
|
|
M = v.shape[ 0 ];
|
|
for ( i = 0; i < M; i++ ) {
|
|
for ( j = 0; j < i; j++ ) {
|
|
if ( v.get( i, j ) !== v.get( j, i ) ) {
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
|
|
// EXPORTS //
|
|
|
|
module.exports = isSymmetricMatrix;
|