/*
    * 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.analysis.differentiation;
  
  import org.hipparchus.exception.LocalizedCoreFormats;
  import org.hipparchus.exception.MathIllegalArgumentException;
  import org.hipparchus.util.FastMath;
  import org.hipparchus.util.MathArrays;
  import org.hipparchus.util.MathUtils;
  
  /** Class representing both the value and the differentials of a function.
   * <p>This class is a stripped-down version of {@link DerivativeStructure}
   * with only one {@link DerivativeStructure#getFreeParameters() free parameter}
   * and {@link DerivativeStructure#getOrder() derivation order} also limited to one.
   * It should have less overhead than {@link DerivativeStructure} in its domain.</p>
   * <p>This class is an implementation of Rall's numbers. Rall's numbers are an
   * extension to the real numbers used throughout mathematical expressions; they hold
   * the derivative together with the value of a function.</p>
   * <p>{@link UnivariateDerivative1} instances can be used directly thanks to
   * the arithmetic operators to the mathematical functions provided as
   * methods by this class (+, -, *, /, %, sin, cos ...).</p>
   * <p>Implementing complex expressions by hand using these classes is
   * a tedious and error-prone task but has the advantage of having no limitation
   * on the derivation order despite not requiring users to compute the derivatives by
   * themselves.</p>
   * <p>Instances of this class are guaranteed to be immutable.</p>
   * @see DerivativeStructure
   * @see UnivariateDerivative2
   * @see Gradient
   * @see FieldDerivativeStructure
   * @see FieldUnivariateDerivative1
   * @see FieldUnivariateDerivative2
   * @see FieldGradient
   * @since 1.7
   */
  public class UnivariateDerivative1 extends UnivariateDerivative<UnivariateDerivative1>
          implements Derivative1<UnivariateDerivative1> {
  
      /** The constant value of π as a {@code UnivariateDerivative1}.
       * @since 2.0
       */
      public static final UnivariateDerivative1 PI = new UnivariateDerivative1(FastMath.PI, 0.0);
  
      /** Serializable UID. */
      private static final long serialVersionUID = 20200519L;
  
      /** Value of the function. */
      private final double f0;
  
      /** First derivative of the function. */
      private final double f1;
  
      /** Build an instance with values and derivative.
       * @param f0 value of the function
       * @param f1 first derivative of the function
       */
      public UnivariateDerivative1(final double f0, final double f1) {
          this.f0 = f0;
          this.f1 = f1;
      }
  
      /** Build an instance from a {@link DerivativeStructure}.
       * @param ds derivative structure
       * @exception MathIllegalArgumentException if either {@code ds} parameters
       * is not 1 or {@code ds} order is not 1
       */
      public UnivariateDerivative1(final DerivativeStructure ds) throws MathIllegalArgumentException {
          MathUtils.checkDimension(ds.getFreeParameters(), 1);
          MathUtils.checkDimension(ds.getOrder(), 1);
          this.f0 = ds.getValue();
          this.f1 = ds.getPartialDerivative(1);
      }
  
      /** {@inheritDoc} */
      @Override
      public UnivariateDerivative1 newInstance(final double value) {
          return new UnivariateDerivative1(value, 0.0);
      }
  
      /** {@inheritDoc} */
      @Override
      public UnivariateDerivative1 withValue(final double value) {
          return new UnivariateDerivative1(value, f1);
      }
  
     /** {@inheritDoc} */
     @Override
     public double getValue() {
         return f0;
     }
 
     /** {@inheritDoc} */
     @Override
     public double getDerivative(final int n) {
         switch (n) {
             case 0 :
                 return f0;
             case 1 :
                 return f1;
             default :
                 throw new MathIllegalArgumentException(LocalizedCoreFormats.DERIVATION_ORDER_NOT_ALLOWED, n);
         }
     }
 
     /** Get the first derivative.
      * @return first derivative
      * @see #getValue()
      */
     public double getFirstDerivative() {
         return f1;
     }
 
     /** {@inheritDoc} */
     @Override
     public DerivativeStructure toDerivativeStructure() {
         return getField().getConversionFactory().build(f0, f1);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 add(final UnivariateDerivative1 a) {
         return new UnivariateDerivative1(f0 + a.f0, f1 + a.f1);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 subtract(final UnivariateDerivative1 a) {
         return new UnivariateDerivative1(f0 - a.f0, f1 - a.f1);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 multiply(final int n) {
         return new UnivariateDerivative1(f0 * n, f1 * n);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 multiply(final double a) {
         return new UnivariateDerivative1(f0 * a, f1 * a);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 multiply(final UnivariateDerivative1 a) {
         return new UnivariateDerivative1(f0 * a.f0,
                                          MathArrays.linearCombination(f1, a.f0, f0, a.f1));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 divide(final double a) {
         final double inv1 = 1.0 / a;
         return new UnivariateDerivative1(f0 * inv1, f1 * inv1);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 divide(final UnivariateDerivative1 a) {
         final double inv1 = 1.0 / a.f0;
         final double inv2 = inv1 * inv1;
         return new UnivariateDerivative1(f0 * inv1,
                                          MathArrays.linearCombination(f1, a.f0, -f0, a.f1) * inv2);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 remainder(final UnivariateDerivative1 a) {
 
         // compute k such that lhs % rhs = lhs - k rhs
         final double rem = FastMath.IEEEremainder(f0, a.f0);
         final double k   = FastMath.rint((f0 - rem) / a.f0);
 
         return new UnivariateDerivative1(rem, f1 - k * a.f1);
 
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 negate() {
         return new UnivariateDerivative1(-f0, -f1);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 abs() {
         if (Double.doubleToLongBits(f0) < 0) {
             // we use the bits representation to also handle -0.0
             return negate();
         } else {
             return this;
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 copySign(final UnivariateDerivative1 sign) {
         long m = Double.doubleToLongBits(f0);
         long s = Double.doubleToLongBits(sign.f0);
         if ((m >= 0 && s >= 0) || (m < 0 && s < 0)) { // Sign is currently OK
             return this;
         }
         return negate(); // flip sign
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 copySign(final double sign) {
         long m = Double.doubleToLongBits(f0);
         long s = Double.doubleToLongBits(sign);
         if ((m >= 0 && s >= 0) || (m < 0 && s < 0)) { // Sign is currently OK
             return this;
         }
         return negate(); // flip sign
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 scalb(final int n) {
         return new UnivariateDerivative1(FastMath.scalb(f0, n), FastMath.scalb(f1, n));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 hypot(final UnivariateDerivative1 y) {
 
         if (Double.isInfinite(f0) || Double.isInfinite(y.f0)) {
             return new UnivariateDerivative1(Double.POSITIVE_INFINITY, 0.0);
         } else if (Double.isNaN(f0) || Double.isNaN(y.f0)) {
             return new UnivariateDerivative1(Double.NaN, 0.0);
         } else {
 
             final int expX = getExponent();
             final int expY = y.getExponent();
             if (expX > expY + 27) {
                 // y is negligible with respect to x
                 return abs();
             } else if (expY > expX + 27) {
                 // x is negligible with respect to y
                 return y.abs();
             } else {
 
                 // find an intermediate scale to avoid both overflow and underflow
                 final int middleExp = (expX + expY) / 2;
 
                 // scale parameters without losing precision
                 final UnivariateDerivative1 scaledX = scalb(-middleExp);
                 final UnivariateDerivative1 scaledY = y.scalb(-middleExp);
 
                 // compute scaled hypotenuse
                 final UnivariateDerivative1 scaledH =
                         scaledX.multiply(scaledX).add(scaledY.multiply(scaledY)).sqrt();
 
                 // remove scaling
                 return scaledH.scalb(middleExp);
 
             }
 
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 compose(final double... f) {
         MathUtils.checkDimension(f.length, getOrder() + 1);
         return compose(f[0], f[1]);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 compose(final double ff0, final double ff1) {
         return new UnivariateDerivative1(ff0, this.f1 * ff1);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1Field getField() {
         return UnivariateDerivative1Field.getInstance();
     }
 
     /** Compute a<sup>x</sup> where a is a double and x a {@link UnivariateDerivative1}
      * @param a number to exponentiate
      * @param x power to apply
      * @return a<sup>x</sup>
      */
     public static UnivariateDerivative1 pow(final double a, final UnivariateDerivative1 x) {
         if (a == 0) {
             return x.getField().getZero();
         } else {
             final double aX = FastMath.pow(a, x.f0);
             return new UnivariateDerivative1(aX, FastMath.log(a) * aX * x.f1);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 pow(final double p) {
         if (p == 0) {
             return getField().getOne();
         } else {
             final double f0Pm1 = FastMath.pow(f0, p - 1);
             return compose(f0Pm1 * f0, p * f0Pm1);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 pow(final int n) {
         if (n == 0) {
             return getField().getOne();
         } else {
             final double f0Nm1 = FastMath.pow(f0, n - 1);
             return compose(f0Nm1 * f0, n * f0Nm1);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 atan2(final UnivariateDerivative1 x) {
         final double inv = 1.0 / (f0 * f0 + x.f0 * x.f0);
         return new UnivariateDerivative1(FastMath.atan2(f0, x.f0),
                                          MathArrays.linearCombination(x.f0, f1, -x.f1, f0) * inv);
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 toDegrees() {
         return new UnivariateDerivative1(FastMath.toDegrees(f0), FastMath.toDegrees(f1));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 toRadians() {
         return new UnivariateDerivative1(FastMath.toRadians(f0), FastMath.toRadians(f1));
     }
 
     /** Evaluate Taylor expansion a univariate derivative.
      * @param delta parameter offset Δx
      * @return value of the Taylor expansion at x + Δx
      */
     public double taylor(final double delta) {
         return f0 + delta * f1;
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final UnivariateDerivative1[] a, final UnivariateDerivative1[] b) {
 
         // extract values and first derivatives
         final int      n  = a.length;
         final double[] a0 = new double[n];
         final double[] b0 = new double[n];
         final double[] a1 = new double[2 * n];
         final double[] b1 = new double[2 * n];
         for (int i = 0; i < n; ++i) {
             final UnivariateDerivative1 ai = a[i];
             final UnivariateDerivative1 bi = b[i];
             a0[i]         = ai.f0;
             b0[i]         = bi.f0;
             a1[2 * i]     = ai.f0;
             a1[2 * i + 1] = ai.f1;
             b1[2 * i]     = bi.f1;
             b1[2 * i + 1] = bi.f0;
         }
 
         return new UnivariateDerivative1(MathArrays.linearCombination(a0, b0),
                                          MathArrays.linearCombination(a1, b1));
 
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final double[] a, final UnivariateDerivative1[] b) {
 
         // extract values and first derivatives
         final int      n  = b.length;
         final double[] b0 = new double[n];
         final double[] b1 = new double[n];
         for (int i = 0; i < n; ++i) {
             b0[i] = b[i].f0;
             b1[i] = b[i].f1;
         }
 
         return new UnivariateDerivative1(MathArrays.linearCombination(a, b0),
                                          MathArrays.linearCombination(a, b1));
 
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final UnivariateDerivative1 a1, final UnivariateDerivative1 b1,
                                                    final UnivariateDerivative1 a2, final UnivariateDerivative1 b2) {
         return new UnivariateDerivative1(MathArrays.linearCombination(a1.f0, b1.f0,
                                                                       a2.f0, b2.f0),
                                          MathArrays.linearCombination(a1.f0, b1.f1,
                                                                       a1.f1, b1.f0,
                                                                       a2.f0, b2.f1,
                                                                       a2.f1, b2.f0));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final double a1, final UnivariateDerivative1 b1,
                                                    final double a2, final UnivariateDerivative1 b2) {
         return new UnivariateDerivative1(MathArrays.linearCombination(a1, b1.f0,
                                                                       a2, b2.f0),
                                          MathArrays.linearCombination(a1, b1.f1,
                                                                       a2, b2.f1));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final UnivariateDerivative1 a1, final UnivariateDerivative1 b1,
                                                    final UnivariateDerivative1 a2, final UnivariateDerivative1 b2,
                                                    final UnivariateDerivative1 a3, final UnivariateDerivative1 b3) {
         return new UnivariateDerivative1(MathArrays.linearCombination(a1.f0, b1.f0,
                                                                       a2.f0, b2.f0,
                                                                       a3.f0, b3.f0),
                                          MathArrays.linearCombination(new double[] {
                                                                           a1.f0, a1.f1,
                                                                           a2.f0, a2.f1,
                                                                           a3.f0, a3.f1
                                                                       }, new double[] {
                                                                           b1.f1, b1.f0,
                                                                           b2.f1, b2.f0,
                                                                           b3.f1, b3.f0
                                                                       }));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final double a1, final UnivariateDerivative1 b1,
                                                    final double a2, final UnivariateDerivative1 b2,
                                                    final double a3, final UnivariateDerivative1 b3) {
         return new UnivariateDerivative1(MathArrays.linearCombination(a1, b1.f0,
                                                                       a2, b2.f0,
                                                                       a3, b3.f0),
                                          MathArrays.linearCombination(a1, b1.f1,
                                                                       a2, b2.f1,
                                                                       a3, b3.f1));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final UnivariateDerivative1 a1, final UnivariateDerivative1 b1,
                                                    final UnivariateDerivative1 a2, final UnivariateDerivative1 b2,
                                                    final UnivariateDerivative1 a3, final UnivariateDerivative1 b3,
                                                    final UnivariateDerivative1 a4, final UnivariateDerivative1 b4) {
         return new UnivariateDerivative1(MathArrays.linearCombination(a1.f0, b1.f0,
                                                                       a2.f0, b2.f0,
                                                                       a3.f0, b3.f0,
                                                                       a4.f0, b4.f0),
                                          MathArrays.linearCombination(new double[] {
                                                                           a1.f0, a1.f1,
                                                                           a2.f0, a2.f1,
                                                                           a3.f0, a3.f1,
                                                                           a4.f0, a4.f1
                                                                       }, new double[] {
                                                                           b1.f1, b1.f0,
                                                                           b2.f1, b2.f0,
                                                                           b3.f1, b3.f0,
                                                                           b4.f1, b4.f0
                                                                       }));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 linearCombination(final double a1, final UnivariateDerivative1 b1,
                                                    final double a2, final UnivariateDerivative1 b2,
                                                    final double a3, final UnivariateDerivative1 b3,
                                                    final double a4, final UnivariateDerivative1 b4) {
         return new UnivariateDerivative1(MathArrays.linearCombination(a1, b1.f0,
                                                                       a2, b2.f0,
                                                                       a3, b3.f0,
                                                                       a4, b4.f0),
                                          MathArrays.linearCombination(a1, b1.f1,
                                                                       a2, b2.f1,
                                                                       a3, b3.f1,
                                                                       a4, b4.f1));
     }
 
     /** {@inheritDoc} */
     @Override
     public UnivariateDerivative1 getPi() {
         return PI;
     }
 
     /** Test for the equality of two univariate derivatives.
      * <p>
      * univariate derivatives are considered equal if they have the same derivatives.
      * </p>
      * @param other Object to test for equality to this
      * @return true if two univariate derivatives are equal
      */
     @Override
     public boolean equals(Object other) {
 
         if (this == other) {
             return true;
         }
 
         if (other instanceof UnivariateDerivative1) {
             final UnivariateDerivative1 rhs = (UnivariateDerivative1) other;
             return f0 == rhs.f0 && f1 == rhs.f1;
         }
 
         return false;
 
     }
 
     /** Get a hashCode for the univariate derivative.
      * @return a hash code value for this object
      */
     @Override
     public int hashCode() {
         return 453 - 19 * Double.hashCode(f0) + 37 * Double.hashCode(f1);
     }
 
     /** {@inheritDoc}
      * <p>
      * Comparison performed considering that derivatives are intrinsically linked to monomials in the corresponding
      * Taylor expansion and that the higher the degree, the smaller the term.
      * </p>
      * @since 3.0
      */
     @Override
     public int compareTo(final UnivariateDerivative1 o) {
         final int cF0 = Double.compare(f0, o.getReal());
         if (cF0 == 0) {
             return Double.compare(f1, o.getFirstDerivative());
         } else {
             return cF0;
         }
     }
 
 }