[eigen] About performance with 3-double vectors and self written library

[William Oquendo <woquendo@xxxxxxxxx>]

Dear all,

I have written a small 3 dimensional - double - vector library, and I was expecting that eigen performance was better than my library.. Unfortunately, that is not the case. I have run a test and, for g++ 4.2 I got aprox 12 secons with eigen and aprox 6 seconds with my library. With g++ 4.5, I got 5.5 aprox for eigen and 7 aprox for my library.

I wluld like to know if I am using eigen the wrong way and that is the cause of this c++4.2 performance penalty (I do not have access to g++ 4.5 on the production servers) or this is just an special case.

I am attaching the code and copying  it here:

#include "vector3d.hh"
#include <eigen2/Eigen/Core>
#include <eigen2/Eigen/Geometry>
USING_PART_OF_NAMESPACE_EIGEN
#include <iostream>

using namespace std;

typedef Vector3D vec_t; // my library
//typedef Vector3d vec_t; // Eigen

const double STEPS = 1.0e4; 

int main(void)
{
  double i;
  vec_t v1, v2;
  vec_t v3 = v2;

  vec_t v5;
  ///*
  for(double j = 0; j < STEPS; j++) {
    v3 = v2;    
    // copy constructor
    for(i = 0; i < STEPS; i++) {
      vec_t v4 = v3;
    }
    // copy
    for(i = 0; i < STEPS; i++) {

      v3 = vec_t(i/0.34, i, i*i);
    }
    // accessing one element
    for(i = 0; i < STEPS; i++) {
      v3[1] = i;
    }
    // long airhmetic operations
    v1 = vec_t(1,2.2,3.4);
    v2 = vec_t(-2, 3, 3);

    for(i = 0; i < STEPS; i++) {
      v3 = vec_t(i/0.34, i, i*i);
      v5 = v1+v2-v3;
    }  
    // scalar product
    double result;
    for(i = 0; i < STEPS; i++) {
      result = v3.dot(v5);

    }  
    // cross product
    for(i = 0; i < STEPS; i++) {
      v5 = v1.cross(v2);
    }  
    // complex operation
    for(i = 0; i < 10*STEPS; i++) {
      v5 = v1 + 2.0*v2 - v3/4.0 + (v3.cross(v2));

    }  
    // normalize
    for(i = 0; i < STEPS; i++) {
      v3 = v5.normalized();
    }
    for(i = 0; i < STEPS; i++) {
      v5.normalize();
    }
  }
  //*/
  clog << v1 << endl;

  clog << v2 << endl;
  clog << v3 << endl;
  clog << v5 << endl;
  return 0;
}



Best regards / Cordialmente,

--
William Oquendo
Phd Candidate

Simulation Of Physical Systems Group
National University of Colombia
Linux User # 321481
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Este correo puede carecer de tildes o eñes ya que el teclado no contiene estos caracteres. Presento excusas por eso. 

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Attachment: test.cpp
Description: Binary data

Attachment: vector3d.hh
Description: Binary data