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

#include <iostream>
#include <cmath>



//..................................
// Here is the dot product function 

float dotProduct( float x1, float y1, float z1, float x2, float y2, float z2 )
{
  return (x1*x2) + (y1*y2) + (z1*z2) ;
}




//..................................
// Here is the magnitude function   

float magnitude( float x, float y, float z )
{
  return sqrt( (x*x) + (y*y) + (z*z) ) ;
}



//...........................................
// Now the main program to use the functions 

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 prod ;

  prod =  dotProduct( px1, py1, pz1, px2, py2, pz2 )  ;



  // Calculate the magnitude of each vector 

  float mag1, mag2 ;

  mag1 = magnitude( px1, py1, pz1 ) ;
  mag2 = magnitude( px2, py2, pz2 ) ;



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

  float cosTheta, theta ;

  cosTheta = prod / mag1 / mag2 ;

  theta = acos( cosTheta ) ;

  // .... of course we could have written a function to do this
  // .... last bit , why dont you...

  // Finally print it out 


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

  std::cout << " dprod2: This is the new (slightly) improved version " << std::endl;

  std::cout << " The angle is " 
            << theta 
            << " radians "
            << std::endl ;

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



  return 1 ;
}