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Diffstat (limited to 'src/main/java/org/apache/commons/math3/transform/DftNormalization.java')
-rw-r--r-- | src/main/java/org/apache/commons/math3/transform/DftNormalization.java | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/transform/DftNormalization.java b/src/main/java/org/apache/commons/math3/transform/DftNormalization.java new file mode 100644 index 0000000..db0eddb --- /dev/null +++ b/src/main/java/org/apache/commons/math3/transform/DftNormalization.java @@ -0,0 +1,58 @@ +/* + * 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.math3.transform; + +/** + * This enumeration defines the various types of normalizations that can be applied to discrete + * Fourier transforms (DFT). The exact definition of these normalizations is detailed below. + * + * @see FastFourierTransformer + * @since 3.0 + */ +public enum DftNormalization { + /** + * Should be passed to the constructor of {@link FastFourierTransformer} to use the + * <em>standard</em> normalization convention. This normalization convention is defined as + * follows + * + * <ul> + * <li>forward transform: y<sub>n</sub> = ∑<sub>k=0</sub><sup>N-1</sup> x<sub>k</sub> + * exp(-2πi n k / N), + * <li>inverse transform: x<sub>k</sub> = N<sup>-1</sup> ∑<sub>n=0</sub><sup>N-1</sup> + * y<sub>n</sub> exp(2πi n k / N), + * </ul> + * + * where N is the size of the data sample. + */ + STANDARD, + + /** + * Should be passed to the constructor of {@link FastFourierTransformer} to use the + * <em>unitary</em> normalization convention. This normalization convention is defined as + * follows + * + * <ul> + * <li>forward transform: y<sub>n</sub> = (1 / √N) ∑<sub>k=0</sub><sup>N-1</sup> + * x<sub>k</sub> exp(-2πi n k / N), + * <li>inverse transform: x<sub>k</sub> = (1 / √N) ∑<sub>n=0</sub><sup>N-1</sup> + * y<sub>n</sub> exp(2πi n k / N), + * </ul> + * + * which makes the transform unitary. N is the size of the data sample. + */ + UNITARY; +} |