package org.djutils.math.complex;
   
   /**
    * Complex.java. Immutable complex numbers. This implementation stores the real and imaginary component as a double value. These
    * fields are directly accessible, or through a getter. There are also getters for the norm and phi, but this are a CPU
    * intensive.
    * <p>
    * Copyright (c) 2021-2025 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
    * BSD-style license. See <a href="https://djutils.org/docs/current/djutils/licenses.html">DJUTILS License</a>.
   * </p>
   * @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
   * @author <a href="https://www.tudelft.nl/pknoppers">Peter Knoppers</a>
   */
  public class Complex
  {
      /** Real component. */
      @SuppressWarnings("checkstyle:visibilitymodifier")
      public final double re;
  
      /** Imaginary component. */
      @SuppressWarnings("checkstyle:visibilitymodifier")
      public final double im;
  
      /** The zero value in the complex number space. */
      public static final Complex ZERO = new Complex(0, 0);
  
      /** The (real) one value in the complex number space. */
      public static final Complex ONE = new Complex(1, 0);
  
      /** The (real) minus one value in the complex number space. */
      public static final Complex MINUS_ONE = new Complex(-1, 0);
  
      /** The imaginary unit value (i). */
      public static final Complex I = new Complex(0, 1);
  
      /** The negative imaginary unit value (i). */
      public static final Complex MINUS_I = new Complex(0, -1);
  
      /**
       * Construct a new complex number.
       * @param re real component of the new complex number
       * @param im imaginary component of the new complex number
       */
      public Complex(final double re, final double im)
      {
          this.re = re;
          this.im = im;
      }
  
      /**
       * Construct a new complex number with specified real component and zero imaginary component.
       * @param re the real component of the new complex number
       */
      public Complex(final double re)
      {
          this.re = re;
          this.im = 0;
      }
  
      /**
       * Retrieve the real component of this complex number.
       * @return the real component of this complex number
       */
      public double getRe()
      {
          return this.re;
      }
  
      /**
       * Retrieve the imaginary component of this complex number.
       * @return the imaginary component of this complex number
       */
      public double getIm()
      {
          return this.im;
      }
  
      /**
       * Compute and return the norm, or radius, or absolute value of this complex number.
       * @return the norm, or radius, or absolute value of this complex number. Due to the fact that in this
       *         implementation of complex numbers, all values are stored as a real an imaginary double value; the result may
       *         overflow to Double.POSITIVE_INFINITY, even though both the real and imaginary part of the complex number can be
       *         represented.
       */
      public double norm()
      {
          return hypot(this.re, this.im);
      }
  
      /** Precision limit. */
      private static final double EPSILONSQRT = Math.sqrt(Math.ulp(1.0) / 2);
      /** Square root of smallest floating point value. */
      private static final double SQRT_OF_MIN_VALUE = Math.sqrt(Double.MIN_VALUE);
      /** Square root of biggest floating point value. */
      private static final double SQRT_OF_MAX_VALUE = Math.sqrt(Double.MAX_VALUE);
      
      /**
       * Better implementation of the hypotenuse function (faster and more accurate than the one in the java Math library). <br>
       * Derived from <a href="https://arxiv.org/abs/1904.09481">An improved algorithm for hypot(a, b) by Carlos F. Borges</a>.
      * @param x the x value
      * @param y the y value
      * @return hypot(x, y)
      */
     public static double hypot(final double x, final double y)
     {
         if (x != x || y != y)
         {
             return Double.NaN;
         }
         double absX = Math.abs(x);
         double absY = Math.abs(y);
         if (absX == Double.POSITIVE_INFINITY || absY == Double.POSITIVE_INFINITY)
         {
             return Double.POSITIVE_INFINITY;
         }
         if (absX < absY)
         {
             double swap = absX;
             absX = absY;
             absY = swap;
         }
         if (absY <= absX * EPSILONSQRT)
         {
             return absX;
         }
         double scale = SQRT_OF_MIN_VALUE;
         if (absX > SQRT_OF_MAX_VALUE)
         {
             absX *= scale;
             absY *= scale;
             scale = 1.0 / scale;
         }
         else if (absY < SQRT_OF_MIN_VALUE)
         {
             absX /= scale;
             absY /= scale;
         }
         else
         {
             scale = 1.0;
         }
         double h = Math.sqrt(Math.fma(absX, absX, absY * absY));
         double hsq = h * h;
         double xsq = absX * absX;
         double a = Math.fma(-absY, absY, hsq - xsq) + Math.fma(h, h, -hsq) - Math.fma(absX, absX, -xsq);
         return scale * (h - a / (2.0 * h));
     }
 
     /**
      * Compute and return the phase or phi of this complex number.
      * @return the phase or phi of this complex number in Radians. Due to the fact that in this implementation of
      *         complex numbers, all values are stored as a real and imaginary value; the result of this method is always
      *         normalized to the interval (-&pi;,&pi;].
      */
     public double phi()
     {
         return Math.atan2(this.im, this.re);
     }
 
     /**
      * Determine if this Complex has an imaginary component of zero.
      * @return true if the imaginary component of this Complex number is 0.0; false if the imaginary component of this
      *         Complex number is not 0.0.
      */
     public boolean isReal()
     {
         return this.im == 0.0;
     }
 
     /**
      * Determine if this Complex has a real component of zero.
      * @return true if the real component of this Complex number is 0.0; false if the real component of this Complex
      *         number is not 0.0
      */
     public boolean isImaginary()
     {
         return this.re == 0.0;
     }
 
     /**
      * Construct the complex conjugate of this Complex.
      * @return the complex conjugate of this
      */
     public Complex conjugate()
     {
         return new Complex(this.re, -this.im);
     }
 
     /**
      * Rotate this Complex by an angle.
      * @param angle the angle (in Radians)
      * @return the result of the rotation
      */
     public Complex rotate(final double angle)
     {
         double sin = Math.sin(angle);
         double cos = Math.cos(angle);
         return new Complex(this.re * cos - this.im * sin, this.im * cos + this.re * sin);
     }
 
     /**
      * Add this Complex and another Complex.
      * @param rightOperand the other Complex
      * @return the sum of this Complex and the other Complex
      */
     public Complex plus(final Complex rightOperand)
     {
         return new Complex(this.re + rightOperand.re, this.im + rightOperand.im);
     }
 
     /**
      * Add a scalar to this Complex.
      * @param rightOperand the scalar
      * @return the sum of this Complex and the scalar
      */
     public Complex plus(final double rightOperand)
     {
         return new Complex(this.re + rightOperand, this.im);
     }
 
     /**
      * Subtract another Complex from this Complex.
      * @param rightOperand the other Complex
      * @return the difference of this Complex and the other Complex
      */
     public Complex minus(final Complex rightOperand)
     {
         return new Complex(this.re - rightOperand.re, this.im - rightOperand.im);
     }
 
     /**
      * Subtract a scalar from this Complex.
      * @param rightOperand the scalar
      * @return the difference of this Complex and the scalar
      */
     public Complex minus(final double rightOperand)
     {
         return new Complex(this.re - rightOperand, this.im);
     }
 
     /**
      * Multiply this Complex with another Complex.
      * @param rightOperand the right hand side operand
      * @return the product of this Complex and the other Complex
      */
     public Complex times(final Complex rightOperand)
     {
         return new Complex(this.re * rightOperand.re - this.im * rightOperand.im,
                 this.im * rightOperand.re + this.re * rightOperand.im);
     }
 
     /**
      * Multiply this Complex with a scalar.
      * @param rightOperand the right hand side operand
      * @return the product of this Complex and the scalar
      */
     public Complex times(final double rightOperand)
     {
         return new Complex(this.re * rightOperand, this.im * rightOperand);
     }
 
     /**
      * Compute the reciprocal of this Complex. If this is zero, the result will have the re field set to
      * Double.POSITIVE_INFINITY and the imaginary part set to NEGATIVE_INFINITY.
      * @return the reciprocal of this Complex (1 / this)
      */
     public Complex reciprocal()
     {
         double divisor = this.re * this.re + this.im * this.im;
         if (0.0 == divisor)
         {
             return new Complex(Double.POSITIVE_INFINITY, Double.POSITIVE_INFINITY);
         }
         return new Complex(this.re / divisor, -this.im / divisor);
     }
 
     /**
      * Divide this Complex by another Complex. Division by ZERO yields a Complex with re set to Infinity if this.re != 0 and NaN
      * if this.re == 0 and im set to Infinity if this.im != 0 and NaN if this.im == 0.
      * @param rightOperand the right hand side operand
      * @return the ratio of this Complex and the right hand side operand
      */
     public Complex divideBy(final Complex rightOperand)
     {
         if (rightOperand.re == 0 && rightOperand.im == 0)
         {
             return new Complex(this.re / 0.0, this.im / 0.0);
         }
         return this.times(rightOperand.reciprocal());
     }
 
     /**
      * Divide this Complex by a scalar. Division by 0.0 yields a Complex with re set to Infinity if this.re != 0 and NaN if
      * this.re == 0 and im set to Infinity if this.im != 0 and NaN if this.im == 0.
      * @param rightOperand the scalar right hand side operand
      * @return the ratio of this Complex and the right hand side operand
      */
     public Complex divideBy(final double rightOperand)
     {
         return new Complex(this.re / rightOperand, this.im / rightOperand);
     }
 
     @Override
     public String toString()
     {
         return "Complex [re=" + this.re + ", im=" + this.im + "]";
     }
 
     @Override
     public int hashCode()
     {
         final int prime = 31;
         int result = 1;
         long temp;
         temp = Double.doubleToLongBits(this.im);
         result = prime * result + (int) (temp ^ (temp >>> 32));
         temp = Double.doubleToLongBits(this.re);
         result = prime * result + (int) (temp ^ (temp >>> 32));
         return result;
     }
 
     @SuppressWarnings("checkstyle:needbraces")
     @Override
     public boolean equals(final Object obj)
     {
         if (this == obj)
             return true;
         if (obj == null)
             return false;
         if (getClass() != obj.getClass())
             return false;
         Complex other = (Complex) obj;
         if (Double.doubleToLongBits(this.im) != Double.doubleToLongBits(other.im))
             return false;
         if (Double.doubleToLongBits(this.re) != Double.doubleToLongBits(other.re))
             return false;
         return true;
     }
 
 }