/* -*-  Mode: Text -*- */

/********************************************************************\
* File: noise.hs                                                     *
* Date: 04/25/1997                                                   *
* Author: Cem Unsal                                                  *
*         Robotics Institute, Carnegie-Mellon University             *
*         unsal@ri.cmu.edu                                           *
*                                                                    *
* Description:                                                       *
* Gaussian random number generator                                   *
* From Nummerical Recipes in C by Press et al.                       *
*                                                                    *
* There are two independent Gasussian signals (y1 and y2)            * 
* with:                                                              *
* mean = 0, variance = 1.0                                           *
*                                                                    *
* The SHIFT (ver 2.10) function random() acts similar to Matlab's    *
* 'rand' function on a Sun4m running SunOS 4.1.4                     *
*                                                                    *
* Natural log function is defined as an external C function. The     *
* function 'ln' described in the Shift manual is not implemented.    *
*                                                                    *
* External C functions: natlog                                       *
*                                                                    *
* This file is distributed under the conditions described in the     *
* file 'CONDITIONS' which should accompany this file.                *
\********************************************************************/

#ifndef SAHS_NOISE_HS
#define SAHS_NOISE_HS

/* External functions */
function natlog(number x) -> number;

type Gaussian
{
   state continuous number x1, x2; 
   state number PI := 3.1415927;
         
   output continuous number sg1, sg2;  // Two independent signals
  
   discrete generate;

   flow default 
     {
       x1 = random();
       x2 = random();
       sg1 = sqrt(-2*natlog(x1)) * cos(2*PI*x2);
       sg2 = sqrt(-2*natlog(x1)) * sin(2*PI*x2);
     };
}

#endif // SAHS_NOISE_HS