Logarithmic function is a function with power (real number) as independent variable, exponent as dependent variable and base constant as constant, also called logarithmic function. "log" is the abbreviation of "logarithm", which means: if a x = n (a > 0, and a≠ 1), then x is the logarithm of n with the base of a, and it is recorded as x=log(a)(N), where a should be written at the lower right of log. Logarithm is the reciprocal of power just as division is the reciprocal of multiplication, and vice versa. This means that the logarithm of a number is an exponent that must produce another fixed number (radix), and in a simple case, it is the logarithmic counting factor in the multiplier. Logarithm and power operations are relative. Logarithm based on 10 is often used as lg, and irrational number e is often used as ln.