package misl;

import java.util.Vector;
import util.*;


/** 

  <p> 
  The DFT scales cosine or sine waves by the values from the
  signal.  This code attempt to show this graphically by outputting
  the data for sine or cosine plots, where the sine and cosine
  functions are scaled by the points over which the DFT is
  calculated.
  </p>

  <p>
  The data is output in gnuplot format, where a blank
  line seperates.
  </p>

 */
public class dft_graph {
   private final int REAL_PART = 1;
   private final int IMAG_PART = 2;

   private final double twoPi = 2 * Math.PI;
   /** Vector object containing the points over which the DFT is calculated */
   private Vector vec;
   /** The plot is calculated from 0..<i>end</i> */
   private float end;

  /**
  <p>
   The dft_graph constructor is passed a Vector of 
   <i>point</i> objects.  This Vector object contains
   the points over which the DFT is calculated.
   </p>
   */
  public dft_graph( Vector v )
  {
    vec = v;
    int len = vec.size();
    point p = (point)(vec.elementAt(len-1));
    end = p.x;
  }


  /**
    <p>
    Calculate the cosine or sine functions, scaled by the
    points over which the DFT is calculated.  A relatively
    small step is used in an attempt to yield a smoother
    graph of the functions.
    </p>

    <p>
    Most Java compilers are too stupid to figure out what
    a loop invariant is, so its coded here by hand.
    </p>

   */
  private void calc( int part )
  {
    int len = vec.size();
    for (int m = 0; m < len; m++) {
      point p = (point)vec.elementAt(m);
      double coef = p.y;
      double loopInv = twoPi * m; // loop invariant
      for (double n = 0; n <= end; n = n + 0.125) {
	double scale = (loopInv * n)/(double)len;

	double y = 0.0;
	if (part == REAL_PART) {
	  y = Math.cos( scale );
	}
	else if (part == IMAG_PART) {
	  y = Math.sin( scale );
	}
	y = coef * y;
	System.out.println(" " + n + "  " + y );
      }
      System.out.println();
    }
  } // calc


  /**
    Output a plot for the real part of the DFT

   */
  public void real_part()
  {
    calc( REAL_PART );
  }

  
  /**
    Output a plot for the imaginary part of the DFT
   */
  public void imag_part()
  {
    calc( IMAG_PART );
  }

}