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Diffstat (limited to 'src/main/java/org/apache/commons/math/stat/descriptive/moment/VectorialCovariance.java')
-rw-r--r-- | src/main/java/org/apache/commons/math/stat/descriptive/moment/VectorialCovariance.java | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math/stat/descriptive/moment/VectorialCovariance.java b/src/main/java/org/apache/commons/math/stat/descriptive/moment/VectorialCovariance.java new file mode 100644 index 0000000..71afc68 --- /dev/null +++ b/src/main/java/org/apache/commons/math/stat/descriptive/moment/VectorialCovariance.java @@ -0,0 +1,152 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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. + */ +package org.apache.commons.math.stat.descriptive.moment; + +import java.io.Serializable; +import java.util.Arrays; + +import org.apache.commons.math.DimensionMismatchException; +import org.apache.commons.math.linear.MatrixUtils; +import org.apache.commons.math.linear.RealMatrix; + +/** + * Returns the covariance matrix of the available vectors. + * @since 1.2 + * @version $Revision: 922714 $ $Date: 2010-03-14 02:35:14 +0100 (dim. 14 mars 2010) $ + */ +public class VectorialCovariance implements Serializable { + + /** Serializable version identifier */ + private static final long serialVersionUID = 4118372414238930270L; + + /** Sums for each component. */ + private final double[] sums; + + /** Sums of products for each component. */ + private final double[] productsSums; + + /** Indicator for bias correction. */ + private final boolean isBiasCorrected; + + /** Number of vectors in the sample. */ + private long n; + + /** Constructs a VectorialCovariance. + * @param dimension vectors dimension + * @param isBiasCorrected if true, computed the unbiased sample covariance, + * otherwise computes the biased population covariance + */ + public VectorialCovariance(int dimension, boolean isBiasCorrected) { + sums = new double[dimension]; + productsSums = new double[dimension * (dimension + 1) / 2]; + n = 0; + this.isBiasCorrected = isBiasCorrected; + } + + /** + * Add a new vector to the sample. + * @param v vector to add + * @exception DimensionMismatchException if the vector does not have the right dimension + */ + public void increment(double[] v) throws DimensionMismatchException { + if (v.length != sums.length) { + throw new DimensionMismatchException(v.length, sums.length); + } + int k = 0; + for (int i = 0; i < v.length; ++i) { + sums[i] += v[i]; + for (int j = 0; j <= i; ++j) { + productsSums[k++] += v[i] * v[j]; + } + } + n++; + } + + /** + * Get the covariance matrix. + * @return covariance matrix + */ + public RealMatrix getResult() { + + int dimension = sums.length; + RealMatrix result = MatrixUtils.createRealMatrix(dimension, dimension); + + if (n > 1) { + double c = 1.0 / (n * (isBiasCorrected ? (n - 1) : n)); + int k = 0; + for (int i = 0; i < dimension; ++i) { + for (int j = 0; j <= i; ++j) { + double e = c * (n * productsSums[k++] - sums[i] * sums[j]); + result.setEntry(i, j, e); + result.setEntry(j, i, e); + } + } + } + + return result; + + } + + /** + * Get the number of vectors in the sample. + * @return number of vectors in the sample + */ + public long getN() { + return n; + } + + /** + * Clears the internal state of the Statistic + */ + public void clear() { + n = 0; + Arrays.fill(sums, 0.0); + Arrays.fill(productsSums, 0.0); + } + + /** {@inheritDoc} */ + @Override + public int hashCode() { + final int prime = 31; + int result = 1; + result = prime * result + (isBiasCorrected ? 1231 : 1237); + result = prime * result + (int) (n ^ (n >>> 32)); + result = prime * result + Arrays.hashCode(productsSums); + result = prime * result + Arrays.hashCode(sums); + return result; + } + + /** {@inheritDoc} */ + @Override + public boolean equals(Object obj) { + if (this == obj) + return true; + if (!(obj instanceof VectorialCovariance)) + return false; + VectorialCovariance other = (VectorialCovariance) obj; + if (isBiasCorrected != other.isBiasCorrected) + return false; + if (n != other.n) + return false; + if (!Arrays.equals(productsSums, other.productsSums)) + return false; + if (!Arrays.equals(sums, other.sums)) + return false; + return true; + } + +} |