# How can I optimize vector normalization in a Molecular Modeling program?

willkn at montana.com willkn at montana.com
Mon Nov 8 15:24:07 EST 1999

```Hi, I've been working on a molecular modeling program and have been
trying to improve its performance recently.  I did some profiling and
found that the most time by far (41.4%) was spent in a function which
normalizes a 3-dimensional vector (profiling statistics are given at
the bottom).

I am wondering if anyone has suggestions for optimizing that operation.
Thanks,
William Knight
willkn at montana.com

The definition of the function is given below:

typedef double VTYPE;
typedef VTYPE Vector[3];

////////////////////////////////////////////////////////////////////////
////////
// MakeUnitVector
//
// Reduces a normal vector specified as a set of three coordinates,
// to a unit normal vector of length one.
//
bool MakeUnitVector(Vector v)
{
VTYPE length;

// Calculate the length of the vector
length = (VTYPE)sqrt((v[0]*v[0]) + (v[1]*v[1]) + (v[2]*v[2]));

// if length is zero, bail
if(length == 0)
return false;

// Divide each element by the length to get a unit vector.
v[0] /= length;
v[1] /= length;
v[2] /= length;

return true;
}// MakeUnitVector

//***************** Profiling Details ************//

Func          Func+Child           Hit
Time   %         Time      %      Count  Function
---------------------------------------------------------
15493.876  41.4    15493.876  41.4  9971880 MakeUnitVector(double *
const) (vector.obj)
5951.749  15.9     6789.747  18.1   627030
CForceField::CalcVanderwaalsInteraction(void) (cforcefield.obj)
2185.047   5.8    18425.737  49.2    84010
CForceField::CalcPotentialsAndForces(class CFFPairList *,class
CEEPairList *,class CEOPairList *) (cforcefield.obj)
1976.562   5.3    13039.435  34.8  3752280
CForceField::CalcEEInteraction(class CElectron *,class CElectron *)
(cforcefield.obj)
1778.265   4.7     1778.265   4.7  4656515 VectorMagnitude(double *
const) (vector.obj)
1668.910   4.5     1668.910   4.5  8884682 MultiplyVector(double *
const,double) (vector.obj)
1270.428   3.4     1270.428   3.4 13438760 SubtractVector(double *
const,double * const) (vector.obj)
1195.278   3.2     1195.278   3.2 21288242 AddVector(double *
const,double * const) (vector.obj)
1145.663   3.1     1238.959   3.3       64 CStatus::Print(char *)
(cstatus.obj)

Sent via Deja.com http://www.deja.com/