51 lines
1.7 KiB
C
51 lines
1.7 KiB
C
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2020 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "stdlib/stats/base/smeanli.h"
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#include "stdlib/blas/ext/base/sapxsum.h"
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#include <stdint.h>
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/**
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* Computes the arithmetic mean of a single-precision floating-point strided array using a one-pass trial mean algorithm.
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*
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* ## References
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*
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* - Ling, Robert F. 1974. "Comparison of Several Algorithms for Computing Sample Means and Variances." _Journal of the American Statistical Association_ 69 (348). American Statistical Association, Taylor & Francis, Ltd.: 859–66. doi:[10.2307/2286154](https://doi.org/10.2307/2286154).
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*
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* @param N number of indexed elements
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* @param X input array
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* @param stride stride length
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* @return output value
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*/
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float stdlib_strided_smeanli( const int64_t N, const float *X, const int64_t stride ) {
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int64_t ix;
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if ( N <= 0 ) {
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return 0.0f / 0.0f; // NaN
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}
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if ( N == 1 || stride == 0 ) {
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return X[ 0 ];
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}
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if ( stride < 0 ) {
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ix = (1-N) * stride;
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} else {
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ix = 0;
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}
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return X[ ix ] + (float)( (double)stdlib_strided_sapxsum( N-1, -X[ ix ], X+( (stride > 0) ? stride : 0 ), stride ) / (double)N );
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}
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