commons-math-transform/src/main/java/org/apache/commons/math4/transform/RealTransform.java

/*
 * 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.math4.transform;

import java.util.function.DoubleUnaryOperator;
import java.util.function.UnaryOperator;

/**
 * Real transforms.
 */
public interface RealTransform extends UnaryOperator<double[]> {
    /**
     * Returns the transform of the specified data set.
     *
     * @param f the data array to be transformed (signal).
     * @return the transformed array (spectrum).
     * @throws IllegalArgumentException if the transform cannot be performed.
     */
    double[] apply(double[] f);

    /**
     * Returns the transform of the specified function.
     *
     * @param f Function to be sampled and transformed.
     * @param min Lower bound (inclusive) of the interval.
     * @param max Upper bound (exclusive) of the interval.
     * @param n Number of sample points.
     * @return the result.
     * @throws IllegalArgumentException if the transform cannot be performed.
     */
    default double[] apply(DoubleUnaryOperator f,
                           double min,
                           double max,
                           int n) {
        return apply(TransformUtils.sample(f, min, max, n));
    }
}