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Many properties of the real logarithm also apply to the logarithmic derivative, even when the function does not take values in the positive reals. For example, since the logarithm of a product is the sum of the logarithms of the factors, we have () ′ = ( + ) ′ = () ′ + () ′.
ln(r) is the standard natural logarithm of the real number r. 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].
In calculus, logarithmic differentiation or differentiation by taking logarithms is a method used to differentiate functions by employing the logarithmic derivative of a function f, [1] () ′ = ′ ′ = () ′.
The logarithmic derivative is another way of stating the rule for differentiating the logarithm of a function (using the chain rule): () ′ = ′, wherever is positive. Logarithmic differentiation is a technique which uses logarithms and its differentiation rules to simplify certain expressions before actually applying the derivative.
The logarithmic derivative of the gamma function is called the digamma function; higher derivatives are the polygamma functions. The analog of the gamma function over a finite field or a finite ring is the Gaussian sums, a type of exponential sum. The reciprocal gamma function is an entire function and has been studied as a specific topic.
The digamma function (), visualized using domain coloring Plots of the digamma and the next three polygamma functions along the real line (they are real-valued on the real line) In mathematics, the digamma function is defined as the logarithmic derivative of the gamma function: [1] [2] [3]
For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the 3 rd power: 1000 = 10 3 = 10 × 10 × 10. More generally, if x = b y, then y is the logarithm of x to base b, written log b x, so log 10 1000 = 3. As a single-variable function, the logarithm to base b is the inverse of exponentiation with base b.
All instances of log(x) without a subscript base should be interpreted as a natural logarithm, also commonly written as ln(x) or log e (x). In number theory , an arithmetic , arithmetical , or number-theoretic function [ 1 ] [ 2 ] is generally any function whose domain is the set of positive integers and whose range is a subset of the complex ...