/* University College London Dept of P&A course in C++ 3C59 
| all rights reserved 1999 
|
| Example: Dot Product
|
| "Use of in-built data types to perform 3-vector dot product"
|
| Author: P.Clarke 
*/

#include <iostream>
#include <cmath>

#define PI 3.14159 

int main() {


  // Declare some variables to represent two 3-vectors 

  float px1, py1, pz1 ;
  float px2, py2, pz2 ;


  // Set them to something 
  px1 = 1. ; 
  py1 = 1.5 ;
  pz1 = 1.6 ;

  px2 = -0.3 ;
  py2 = 1.2 ;
  pz2 = 1. ;



  // Take the dot product 

  float dotProduct ;

  dotProduct =  (px1 * px2) + (py1 * py2) + (pz1 * pz2)  ;



  // Calculate the magnitude of each vector 

  float mag1, mag2 ;
  float mag1sq, mag2sq ;

  mag1sq =  (px1 * px1) + (py1 * py1) + (pz1 * pz1)  ;
  mag2sq =  (px2 * px2) + (py2 * py2) + (pz2 * pz2)  ;

  mag1 = sqrt( mag1sq ) ;
  mag2 = sqrt( mag2sq ) ;




  // Calculate the cosine of the angle between the vectors,
  // and then find the angle itself 

  float cosTheta, theta ;

  cosTheta = dotProduct / mag1 / mag2 ;

  theta = acos( cosTheta ) ;


  // Finally print it out 

  std::cout << "TTTTTTTTTTTTTTTT 3C59 example TTTTTTTTTTTTTTTT" << std::endl ;

  std::cout << " dprod1: The angle between the vectors is " 
            << theta 
            << " radians "
            << std::endl ;

  std::cout << "LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL" << std::endl ;



  // Finish by sending back the number 1 to indicate success

  return 1 ;
}