001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    
018    package org.apache.commons.math.analysis;
019    
020    /**
021     * Extension of {@link MultivariateRealFunction} representing a differentiable
022     * multivariate real function.
023     * @version $Revision: 811685 $ $Date: 2009-09-05 19:36:48 +0200 (sam. 05 sept. 2009) $
024     * @since 2.0
025     */
026    public interface DifferentiableMultivariateRealFunction extends MultivariateRealFunction {
027    
028        /**
029         * Returns the partial derivative of the function with respect to a point coordinate.
030         * <p>
031         * The partial derivative is defined with respect to point coordinate
032         * x<sub>k</sub>. If the partial derivatives with respect to all coordinates are
033         * needed, it may be more efficient to use the {@link #gradient()} method which will
034         * compute them all at once.
035         * </p>
036         * @param k index of the coordinate with respect to which the partial
037         * derivative is computed
038         * @return the partial derivative function with respect to k<sup>th</sup> point coordinate
039         */
040        MultivariateRealFunction partialDerivative(int k);
041    
042        /**
043         * Returns the gradient function.
044         * <p>If only one partial derivative with respect to a specific coordinate is
045         * needed, it may be more efficient to use the {@link #partialDerivative(int)} method
046         * which will compute only the specified component.</p>
047         * @return the gradient function
048         */
049        MultivariateVectorialFunction gradient();
050    
051    }