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The principal argument of any positive real number x is 0; hence Log(x) is a real number and equals the real (natural) logarithm. However, the above formulas for logarithms of products and powers do not generalize to the principal value of the complex logarithm. [96]
The natural logarithm of x is generally written as ln x, log e x, or sometimes, if the base e is implicit, simply log x. [2] [3] Parentheses are sometimes added for clarity, giving ln(x), log e (x), or log(x). This is done particularly when the argument to the logarithm is not a single symbol, so as to prevent ambiguity.
Arg(z) is the principal value of the arg function; its value is restricted to (−π, π]. It can be computed using Arg(x + iy) = atan2(y, x). Log(z) is the principal value of the complex logarithm function and has imaginary part in the range (−π, π].
The same formula applies to octonions, with a zero real part and a norm equal to 1. These formulas are a direct generalization of Euler's identity, since and are the only complex numbers with a zero real part and a norm (absolute value) equal to 1.
If x is a nonnegative real number, and n is a positive integer, / or denotes the unique nonnegative real n th root of x, that is, the unique nonnegative real number y such that =. If x is a positive real number, and p q {\displaystyle {\frac {p}{q}}} is a rational number , with p and q > 0 integers, then x p / q {\textstyle x^{p/q}} is defined as
Including 0, the set has a semiring structure (0 being the additive identity), known as the probability semiring; taking logarithms (with a choice of base giving a logarithmic unit) gives an isomorphism with the log semiring (with 0 corresponding to ), and its units (the finite numbers, excluding ) correspond to the positive real numbers.
Evaluations of the digamma function at rational values. [10] The Laurent series expansion for the Riemann zeta function*, where it is the first of the Stieltjes constants. [11] Values of the derivative of the Riemann zeta function and Dirichlet beta function. [12]: 137 [13] In connection to the Laplace and Mellin transform. [14] [15]
The graphs of the functions x ↦ a x are shown for a = 2 (dotted), a = e (blue), and a = 4 (dashed). They all pass through the point (0,1), but the red line (which has slope 1) is tangent to only e x there. The value of the natural log function for argument e, i.e. ln e, equals 1.