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why 1/Double.Epsilon gives infinity?

Posted on 2011-03-02
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Last Modified: 2012-05-11
why 1/Double.Epsilon gives infinity?
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Question by:dadadude
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10 Comments
 
LVL 45

Expert Comment

by:AndyAinscow
ID: 35019856
I was just about to say that in response to your (just deleted) question.
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LVL 45

Expert Comment

by:AndyAinscow
ID: 35019875
Basically epsilon is the smallest number that can be represented by a double, just a fraction above zero.  Trying to divide one by epsilon just isn't handled by the .net framework.

Back to your original question - you need to set a limit below which the function isn't being called, rather than trying to hack around it by adding epsilon
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Author Comment

by:dadadude
ID: 35019879
well the other question was complicated i wanted to make it simpler lol.
i found that on google:
double.Epsilon is denormalized, so it is smaller than 2**(min exponent). There is no equivalent of denormalization for extremely large values, so the reciprocal is too large to be representable.
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Author Comment

by:dadadude
ID: 35019892
Andy what do u mean by:
Back to your original question - you need to set a limit below which the function isn't being called, rather than trying to hack around it by adding epsilon
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Author Comment

by:dadadude
ID: 35019914
Do you mean that there might be something wrong in the function.?
actually sigma is the Standard deviation:
public static double StandardDeviation(List<double> num)
    {
        double SumOfSqrs = 0;

        double avg = num.Average();

        for (int i = 0; i < num.Count; i++)
        {
            SumOfSqrs += Math.Pow(((double)num[i] - avg), 2);
        }

        double n = (double)num.Count;
        if (n == 1)
        {
            return Math.Sqrt(SumOfSqrs);
        }
        else
        {
            return Math.Sqrt(SumOfSqrs / (n - 1));
        }
    }

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Accepted Solution

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AndyAinscow earned 2000 total points
ID: 35019925
Your other question where you attempted to add the value epsilon to prevent a divide by zero error.
Instead you need to check if the value you are going to divide by is below a limit (up to you how much it is) and then return a suitable default value.
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LVL 45

Expert Comment

by:AndyAinscow
ID: 35019949
public static double StandardDeviation(List<double> num)
That looks OK, but that isn't the function in the deleted question:

I am having a problem with non-numerical
if sigma = 0;
it is always giving Non-numerica even if i add Double.Epsilon
   double weight = (1.0 /( Math.Sqrt(2.0 * Math.PI * sigma + Double.Epsilon)+Double.Epsilon))*Math.Exp(-Math.Pow((double)s1.Count-mu,2.0)/(Math.Pow(sigma+Double.Epsilon,2.0)));
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Author Comment

by:dadadude
ID: 35019962
oh ok I understand.
yes i think that you are right.
anyway thanks for your help. always a pleasure.
i finish my work on the code today, i still have to normilize  the matrix.

Take care.
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Author Comment

by:dadadude
ID: 35019974
yes exactly I am computing the gaussian function to weight my values.
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Author Comment

by:dadadude
ID: 35019986
The formula is very complicated . I posted it many times in here. but i got no answer for weeks sometimes.
if u are interested you can check: Levine-nazif Inter cluster contrast and intra-cluster uniformity.
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