/*
    * Licensed to the Hipparchus project under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The Hipparchus project 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
    *
    *      https://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.hipparchus.optim.nonlinear.vector.constrained;
  
  import org.hipparchus.linear.Array2DRowRealMatrix;
  import org.hipparchus.linear.ArrayRealVector;
  import org.hipparchus.linear.RealMatrix;
  import org.hipparchus.linear.RealVector;
  
  public class RosenbrockFunction extends TwiceDifferentiableFunction {
  
      @Override
      public int dim() {
          return 2;
      }
  
      @Override
      public double value(RealVector x) {
          return (1.0-x.getEntry(0))*(1.0-x.getEntry(0))+100.0*(x.getEntry(1)-x.getEntry(0)*x.getEntry(0))*(x.getEntry(1)-x.getEntry(0)*x.getEntry(0));
      }
  
      @Override
      public RealVector gradient(RealVector x) {
          RealVector grad=new ArrayRealVector(x.getDimension());
          grad.setEntry(0,-2.0*(1.0-x.getEntry(0))-400.0*(x.getEntry(1)-x.getEntry(0)*x.getEntry(0))*x.getEntry(0));
          grad.setEntry(1,200.0*(x.getEntry(1)-x.getEntry(0)*x.getEntry(0)));
          return grad;
      }
  
      @Override
      public RealMatrix hessian(RealVector x) {
          RealMatrix h=new Array2DRowRealMatrix(2,2);
          double a00=800.0*x.getEntry(0)*x.getEntry(0)-400.0*(x.getEntry(1)-x.getEntry(0)*x.getEntry(0))+2;
          double a01=-400.0*x.getEntry(0);
          double a10=-400*x.getEntry(0);
          double a11=200;
          h.setEntry(0,0, a00);
          h.setEntry(0,1, a01);
          h.setEntry(1,0, a10);
          h.setEntry(1,1, a11);
          return h;
      }
  
  }