atan
 fatan 

 NAME
  atan    - return arc tan of a double quantity
  fatan   - return arc tan of a float quantity

 SYNOPSIS
  #include <math.h>

  double a = atan(b);
  double b;

  float  c = fatan(d);
  float  d;

 FUNCTION
  Returns the arc tan of a floating point quantity

 EXAMPLE
  /*
   *  compile with the math library -lm
   */

  #include <math.h>
  #include <stdio.h>

  main()
  {
      {
      double a = atan(0.25);
      printf("atan 0.25 = %lfn", a);     /*  0.245   */
      }
      {                       /*  less accuracy   */
      float a = fatan(0.25);
      printf("atan 0.25 = %lfn", (double)a);
      }
      return(0);
  }


 INPUTS
  double b;   double floating point value
  float  d;   float  floating point value

 RESULTS
  double a;   result double floating point value
  float  c;   result float  floating point value