Expert: vijayan - 4/28/2011

Question
But the problem is about Epsilon now ...I am not able its giving error ... I have to include it in driving sample file also ...

am i rite?

Sir i am today doing very much hardwork on these. I am sure at the end of the day i will come with senseible doubts ..

Thank you, Whenever i will stuck i will mail you please help me out

Answer
Slight variations in rounding can change the outcome of exact floating-point comparisons. leading to unexpected or incorrect behavior.

Tests for equality of floating-point quantities should be made within some tolerance (epsilon in this case) related to the expected precision of the calculation

A floating point number N may be as close to 2.0 as can be possible (in the floating point representation that the implementation uses) without actually exactly matching 2.0. Well behaved code uses an inexact or fuzzy comparison to test a value to within a certain tolerance, for example:

epsilon = 0.0000001

if( std::abs( N - 2.0 ) <= epsilon ) // the absolute difference between N and 2.0 is less than epsilon

For more information, see the first part of http://download.oracle.com/docs/cd/E19957-01/806-3568/ncg_goldberg.html


The next question is how do we access epsilon which is defined in one file from another file. This is the basic structure:

epsilon.h - contains the declaration of epsilon, we need the declaration to use it
---------

extern const float epsilon ;



epsilon.cpp - contains the definition of epsilon
-----------

const float epsilon = 0.00000001f ;    


use_epsilon.cpp - file where we want to use epsilon
---------------

#include "epsilon.h" // bring in the declaration of epsilon
#include <cmath> // for std::abs

// now we can use epsilon; for example:

bool is_equal( float a, float b )
{
       return std::abs( a - b ) <= epsilon ;
}

While building, compile epsilon.cpp, compile use_epsilon.cpp, compile the other .cpp files, and link the object files together.

For example, using g++

g++ epsilon.cpp use_epsilon.cpp main.cpp -o myprogram