/*****************************************************************************\
 * MathOps
\*****************************************************************************/

package com.mhuss.AstroLib;

/**
 * MathOps contains some useful trig, vector and matrix operations.
 * 

 * Based on C code by Bill Gray (www.projectpluto.com)
 */
public class MathOps {   // Change to public by Strickling

 /**
  * Calculates the arc cosine, but limits the input to the range
  * ( -1.0 < rad < +1.0 ). 

  * This avoids overflow errors. If the input is <= -1.0 radians,
  * Math.PI is returned. If the input is >= 1.0 radians,
  * 0 is returned.
  *
  * @param arg The angle in radians
  *
  * @return The arc cosine, limited to the range 0 to Pi.
  */
  public static double acose( double arg ) {
    if( arg >= 1D )
      return( 0D );
    else if( arg <= -1D )
      return( Math.PI );
    else
      return( Math.acos( arg ) );
  }

 /**
  * Calculates the arc sine, but limits the input to the range
  * ( -1.0 < rad < +1.0 ). 

  * This avoids overflow errors. If the input is less than
  * -1 (radian), -PI/2 is returned. If the input is greater than
  * 1 (radian), +PI/2 is returned.
  *
  * @param arg The angle in radians
  *
  * @return The arc sine, limited to the range -Pi/2 0 to Pi/2.
  */
  public static double asine( double arg ) {
    if( arg >= 1. )
      return( Astro.PI_OVER_TWO );
    else if( arg <= -1. )
      return( -Astro.PI_OVER_TWO );
    else
      return( Math.asin( arg) );
  }

  // typedef double AstroVector[3];
  public static final int VECTOR_SIZE = 3;

  //typedef double AstroMatrix[9];
  static final int MATRIX_SIZE = 9;

 /**
  * Initializes a matrix to base (identity) values.
  * The matrix is set as follows:
  *   [1][0][0]
  *   [0][1][0]
  *   [0][0][1]
  * 
  *
  * @param matrix The matrix to initialize
  */
  public static void setIdentityMatrix( double matrix[] ) {
    for( int i=0; i
  * Inverting an orthonormal matrix is simple:
  * swap rows and columns, and you're done.
  */
  static void invertOrthonormalMatrix( double matrix[] )
  {
    double temp;

    // swap [1] and [3]
    temp = matrix[1];  matrix[1] = matrix[3];  matrix[3] = temp;
    // swap [2] and [6]
    temp = matrix[2];  matrix[2] = matrix[6];  matrix[6] = temp;
    // swap [5] and [7]
    temp = matrix[5];  matrix[5] = matrix[7];  matrix[7] = temp;
  }

 /**
  * Prespin matrices.
  *
  * @param m1 The first matrix
  * @param m2 The second matrix
  * @param angle The angle to use
  */
  static void preSpinMatrix( double m1[], double m2[], double angle )
  {
    double sinAng = Math.sin( angle );
    double cosAng = Math.cos( angle );
    double tval;

    for( int i=0; i