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* @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';
// MAIN //
/**
* Updates a centroid.
*
* ## Notes
*
* - Uses Welford's algorithm for updating an arithmetic mean.
*
* @private
* @param {PositiveInteger} ndims - number of dimensions
* @param {PositiveInteger} N - number of data points in a cluster
* @param {NumericArray} C - strided array containing centroids
* @param {PositiveInteger} strideC - centroid column stride
* @param {NonNegativeInteger} offsetC - centroid index offset
* @param {NumericArray} V - strided array containing a data point
* @param {integer} strideV - vector stride
* @param {NonNegativeInteger} offsetV - vector index offset
* @returns {NumericArray} strided array containing centroids
*/
function updateCentroid( ndims, N, C, strideC, offsetC, V, strideV, offsetV ) {
var delta;
var ci;
var i;
for ( i = 0; i < ndims; i++ ) {
ci = C[ offsetC ];
delta = V[ offsetV ] - ci;
ci += delta / N;
C[ offsetC ] = ci;
offsetC += strideC;
offsetV += strideV;
}
return C;
}
// EXPORTS //
module.exports = updateCentroid;
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