In mathematics, the logarithmic integral function or integral logarithm li(x) is a special function.It is relevant in problems of physics and has number theoretic significance. In particular, according to the Prime number theorem it is a very good approximation to the prime-counting function, which is defined as the number of prime numbers less than or equal to a given value .

A sigmoid function is a mathematical function having a characteristic "S"-shaped curve or sigmoid curve.. A common example of a sigmoid function is the logistic function shown in the first figure and defined by the formula: = + = + = ().Other standard sigmoid functions are given in the Examples section.In some fields, most notably in the context of artificial neural networks, …

for arbitrary real constants a, b and non-zero c.It is named after the mathematician Carl Friedrich Gauss.The graph of a Gaussian is a characteristic symmetric "bell curve" shape.The parameter a is the height of the curve's peak, b is the position of the center of the peak, and c (the standard deviation, sometimes called the Gaussian RMS width) controls the width of the "bell".

Notation. The ISO 80000-2 standard abbreviations consist of ar-followed by the abbreviation of the corresponding hyperbolic function (e.g., arsinh, arcosh). The prefix arc-followed by the corresponding hyperbolic function (e.g., arcsinh, arccosh) is also commonly seen, by analogy with the nomenclature for inverse trigonometric functions.These are misnomers, since the …

The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion.There may be 2 trillion galaxies in …

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The complex logarithm is the complex number analogue of the logarithm function. No single valued function on the complex plane can satisfy the normal rules for logarithms. However, a multivalued function can be defined which satisfies most of the identities. It is usual to consider this as a function defined on a Riemann surface.

Rounding means replacing a number with an approximate value that has a shorter, simpler, or more explicit representation.For example, replacing $23.4476 with $23.45, the fraction 312/937 with 1/3, or the expression √ 2 with 1.414.. Rounding is often done to obtain a value that is easier to report and communicate than the original. Rounding can also be important to avoid …

Calculus, originally called infinitesimal calculus or "the calculus of infinitesimals", is the mathematical study of continuous change, in the same way that geometry is the study of shape, and algebra is the study of generalizations of arithmetic operations.. It has two major branches, differential calculus and integral calculus; the former concerns instantaneous rates of change, …

The first fundamental theorem may be interpreted as follows. For a continuous function y = f(x) whose graph is plotted as a curve, each value of x has a corresponding area function A(x), representing the area beneath the curve between 0 and x.The area A(x) may not be easily computable, but it is assumed to be well-defined.. The area under the curve between x and x + …