method

lgamma

v1_9_3_392 - Show latest stable - Class: Math

lgamma(p1)

public

Calculates the logarithmic gamma of x and the sign of gamma of x.

Math.lgamma(x) is same as

[Math.log(Math.gamma(x).abs), Math.gamma(x) < 0 ? -1 : 1]

but avoid overflow by Math.gamma(x) for large x.

static VALUE
math_lgamma(VALUE obj, VALUE x)
{
    double d0, d;
    int sign=1;
    VALUE v;
    Need_Float(x);
    d0 = RFLOAT_VALUE(x);
    /* check for domain error */
    if (isinf(d0)) {
        if (signbit(d0)) domain_error("lgamma");
        return rb_assoc_new(DBL2NUM(INFINITY), INT2FIX(1));
    }
    d = lgamma_r(d0, &sign);
    v = DBL2NUM(d);
    return rb_assoc_new(v, INT2FIX(sign));
}

lgamma

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