CODEWITHSUNDEEP
mathinteger-overflowfunction-approximation
Leo
Leo

Reputation: 509

Error in function approximation (OverflowError: int too large to convert to float)

I have written a simple code to approximate exponential integral function (Ei function). This function has already been implemented in other libraries (like mpmath) but for some reasons, I do not want to use them. In this approximation there are some mathematical implementation (like factorial). My code works fine for relatively small values when the number of required terms for function approximation is less than 100 but for approximation of large numbers (For example 200) I need to increase the number of terms to above 200-300 terms. In these cases I get this error:

OverflowError: int too large to convert to float

I also searched about this error. People have suggested to use Decimal to resolve this issue but I could not get it to work. I appreciate any help to fix this issue. Here is my code:

#This code has been  written for approximation of Ei(200) with 150 terms that gives the error

import numpy as np

gamma = 0.5772156649  # gamma is a constant

def Ei(X, k, b):  # Ei (X: number , k : number of terms in approximation, b: Approximation of entire function which is part of approximation)

    for s in range(1, k + 1):  # Factorial
        fact = 1
        for i in range(1, s + 1):
            fact = fact * i

        b += (pow(-1., s + 1) * pow(-X, s) / (s * fact))

    return gamma + np.log(X) - b

# Compare with Ei function in mpmath
from mpmath import ei

print (ei(200))

B = Ei(200, 150, 0)  # Gives OverflowError Error
print (B)

Upvotes: 0

Views: 91

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