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In mathematics, the logarithm of a number is the exponent by which another fixed value, the base, must be raised to produce that number.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.
In mathematics, for given real numbers a and b, the logarithm log b a is a number x such that b x = a.Analogously, in any group G, powers b k can be defined for all integers k, and the discrete logarithm log b a is an integer k such that b k = a.
The natural logarithm of a number is its logarithm to the base of the mathematical constant e, which is an irrational and transcendental number approximately equal to 2.718 281 828 459. [1]
The exponential of a matrix A is defined by =!. Given a matrix B, another matrix A is said to be a matrix logarithm of B if e A = B.. Because the exponential function is not bijective for complex numbers (e.g. = =), numbers can have multiple complex logarithms, and as a consequence of this, some matrices may have more than one logarithm, as explained below.
Napier's "logarithm" is related to the natural logarithm by the relation ()and to the common logarithm by ().Note that and (). Napierian logarithms are essentially natural logarithms with decimal points shifted 7 places rightward and with sign reversed.
Title page of John Napier's Mirifici Logarithmorum Canonis Descriptio from 1614, the first published table of logarithms A page from Napier's Mirifici logarithmorum tables, with trigonometric and log trig data for 34 degrees
Graph of log 2 x as a function of a positive real number x. In mathematics, the binary logarithm (log 2 n) is the power to which the number 2 must be raised to obtain the value n.
Figure 1. Demonstrating log* 4 = 2 for the base-e iterated logarithm. The value of the iterated logarithm can be found by "zig-zagging" on the curve y = log b (x) from the input n, to the interval [0,1].