CODEWITHSUNDEEP
iosmathios7
Adam Knights
Adam Knights

Reputation: 2151

Calculate factorial of a decimal (i.e. Gamma function) on iOS

I need to calculate the factorial of a decimal number, say 6.4, on iOS. I tried

double myFactorial = gamma(6.4);

But get the error "'gamma is unavailable': not avaiable on iOS". Is there a way to add the gamma function into iOS?

Upvotes: 2

Views: 1197

Answers (2)

Sport
Sport

Reputation: 8965

you can try like this logic may be this will well you.
- (int)factorial:(int)operand
{
    if`enter code here`(operand < 0)
        return -1;
    else if (operand > 1)
        return operand * [self factorial:operand - 1];
    else
        return 1;
}

and then 

- (double)factorial:(double)operand
{
    double output = operand;

    if      (output == 0) output = 1; // factorial of 0 is 1
    else if (output < 0)  output = NAN;
    else if (output > 0)
    {
        if (fmod(output, floor(output)) == 0) // integer
            output = round(exp(lgamma(output + 1)));
        else // natural number
            output = exp(lgamma(output + 1));
    }

    return output;
}

- (double)n:(double)n chooseR:(double)r
{
    return round(exp((lgamma(n+1)) - (lgamma(r+1) + lgamma(n-r+1))));
}

- (double)n:(double)n pickR:(double)r
{
    return round(exp(lgamma(n+1) - lgamma(n-r+1)));
}

Upvotes: 0

Antonio MG
Antonio MG

Reputation: 20410

Have you tried:

tgamma(6.4)

I see it working in my code.

There's also:

double tgamma (double x)
float tgammaf (float x)
long double tgammal (long double x)

Upvotes: 3

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