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+/*
+ * 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;
+
+import org.apache.commons.math3.analysis.UnivariateFunction;
+import org.apache.commons.math3.exception.MathIllegalArgumentException;
+import org.apache.commons.math3.exception.NonMonotonicSequenceException;
+import org.apache.commons.math3.exception.NotStrictlyPositiveException;
+
+/**
+ * Interface for one-dimensional data sets transformations producing real results.
+ *
+ * <p>Such transforms include {@link FastSineTransformer sine transform}, {@link
+ * FastCosineTransformer cosine transform} or {@link FastHadamardTransformer Hadamard transform}.
+ * {@link FastFourierTransformer Fourier transform} is of a different kind and does not implement
+ * this interface since it produces {@link org.apache.commons.math3.complex.Complex} results instead
+ * of real ones.
+ *
+ * @since 2.0
+ */
+public interface RealTransformer {
+
+    /**
+     * Returns the (forward, inverse) transform of the specified real data set.
+     *
+     * @param f the real data array to be transformed (signal)
+     * @param type the type of transform (forward, inverse) to be performed
+     * @return the real transformed array (spectrum)
+     * @throws MathIllegalArgumentException if the array cannot be transformed with the given type
+     *     (this may be for example due to array size, which is constrained in some transforms)
+     */
+    double[] transform(double[] f, TransformType type) throws MathIllegalArgumentException;
+
+    /**
+     * Returns the (forward, inverse) transform of the specified real function, sampled on the
+     * specified interval.
+     *
+     * @param f the function to be sampled and transformed
+     * @param min the (inclusive) lower bound for the interval
+     * @param max the (exclusive) upper bound for the interval
+     * @param n the number of sample points
+     * @param type the type of transform (forward, inverse) to be performed
+     * @return the real transformed array
+     * @throws NonMonotonicSequenceException if the lower bound is greater than, or equal to the
+     *     upper bound
+     * @throws NotStrictlyPositiveException if the number of sample points is negative
+     * @throws MathIllegalArgumentException if the sample cannot be transformed with the given type
+     *     (this may be for example due to sample size, which is constrained in some transforms)
+     */
+    double[] transform(UnivariateFunction f, double min, double max, int n, TransformType type)
+            throws NonMonotonicSequenceException,
+                    NotStrictlyPositiveException,
+                    MathIllegalArgumentException;
+}