include/maths.h

   1 /* -*- mode: c; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; c-file-style: "stroustrup"; -*-
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  36
  37 #ifndef _maths_h
  38 #define _maths_h
  39
  40 #ifdef HAVE_CONFIG_H
  41 #include <config.h>
  42 #endif
  43
  44 #include <math.h>
  45 #include "types/simple.h"
  46 #include "typedefs.h"
  47
  48 #ifndef M_PI
  49 #define M_PI            3.14159265358979323846
  50 #endif
  51
  52 #ifndef M_PI_2
  53 #define M_PI_2          1.57079632679489661923
  54 #endif
  55
  56 #ifndef M_2PI
  57 #define M_2PI           6.28318530718
  58 #endif
  59
  60 #ifndef M_SQRT2
  61 #define M_SQRT2 sqrt(2.0)
  62 #endif
  63
  64 #ifdef __cplusplus
  65 extern "C" {
  66 #endif
  67
  68 extern  int             gmx_nint(real a);
  69 extern  real            sign(real x,real y);
  70
  71 extern  real            gmx_erf(real x);
  72 extern  real            gmx_erfc(real x);
  73
  74 /*! \brief Check if two numbers are within a tolerance
  75  *
  76  *  This routine checks if the relative difference between two numbers is
  77  *  approximately within the given tolerance, defined as
  78  *  fabs(f1-f2)<=tolerance*fabs(f1+f2+1.0).
  79  *
  80  *  This expression is somewhat based on trial-and-error; the fabs() term on
  81  *  the right hand side avoids a division (important if f1==f2==0), and adding
  82  *  1.0 is necessary when comparing a single number vs. 0.0.
  83  *
  84  *  To check if two floating-point numbers are almost identical, use this routine
  85  *  with the tolerance GMX_REAL_EPS, or GMX_DOUBLE_EPS if the check should be
  86  *  done in double regardless of Gromacs precision.
  87  *
  88  *  To check if two algorithms produce similar results you will normally need
  89  *  to relax the tolerance significantly since many operations (e.g. summation)
  90  *  accumulate floating point errors.
  91  *
  92  *  \param f1  First number to compare
  93  *  \param f2  Second number to compare
  94  *  \param tol Tolerance to use
  95  *
  96  *  \return 1 if the relative difference is within tolerance, 0 if not.
  97  */
  98 static int
  99 gmx_within_tol(double   f1,
 100                double   f2,
 101                double   tol)
 102 {
 103     /* The or-equal is important - otherwise we return false if f1==f2==0 */
 104     if( fabs(f1-f2) <= tol*0.5*(fabs(f1)+fabs(f2)) )
 105     {
 106         return 1;
 107     }
 108     else
 109     {
 110         return 0;
 111     }
 112 }
 113
 114
 115
 116 /**
 117  * Check if a number is smaller than some preset safe minimum
 118  * value, currently defined as GMX_REAL_MIN/GMX_REAL_EPS.
 119  *
 120  * If a number is smaller than this value we risk numerical overflow
 121  * if any number larger than 1.0/GMX_REAL_EPS is divided by it.
 122  *
 123  * \return 1  if 'almost' numerically zero, 0 otherwise.
 124  */
 125 static int
 126 gmx_numzero(double a)
 127 {
 128   return gmx_within_tol(a,0.0,GMX_REAL_MIN/GMX_REAL_EPS);
 129 }
 130
 131
 132 static real
 133 gmx_log2(real x)
 134 {
 135   const real iclog2 = 1.0/log( 2.0 );
 136
 137     return log( x ) * iclog2;
 138 }
 139
 140
 141 #ifdef __cplusplus
 142 }
 143 #endif
 144
 145 #endif  /* _maths_h */