method

log

v1_9_1_378 - Show latest stable - Class: Math

log(p1, p2 = v2)

public

Returns the natural logarithm of numeric. If additional second argument is given, it will be the base of logarithm.

static VALUE
math_log(int argc, VALUE *argv)
{
    VALUE x, base;
    double d0, d;

    rb_scan_args(argc, argv, "11", &x, &base);
    Need_Float(x);
    errno = 0;
    d0 = RFLOAT_VALUE(x);
    d = log(d0);
    if (argc == 2) {
        Need_Float(base);
        d /= log(RFLOAT_VALUE(base));
    }
    domain_check(d0, d, "log");
    infinity_check(x, d, "log");
    return DBL2NUM(d);
}

1Note

Any base logarithm

szeryf · Jul 13, 20091 thank

Using basic arithmetic you can get logarithm with any base:

def log_with_base base, num
Math.log(num) / Math.log(base)
end

Examples:

>> log_with_base 2, 10
=> 3.32192809488736
>> log_with_base 2, 2
=> 1.0
>> log_with_base 2, 4
=> 2.0
>> log_with_base 2, 16
=> 4.0
>> log_with_base 4, 16
=> 2.0

log

1Note

Any base logarithm

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