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However, a more restricted meaning is often used, where a functional equation is an equation that relates several values of the same function. For example, the logarithm functions are essentially characterized by the logarithmic functional equation log ( x y ) = log ( x ) + log ( y ) . {\displaystyle \log(xy)=\log(x)+\log(y).}
The expression (,) (read: "the map taking x to f of x comma t nought") represents this new function with just one argument, whereas the expression f(x 0, t 0) refers to the value of the function f at the point (x 0, t 0).
That is, a functional differential equation is an equation that contains a function and some of its derivatives evaluated at different argument values. [1] Functional differential equations find use in mathematical models that assume a specified behavior or phenomenon depends on the present as well as the past state of a system. [2]
It is particularly common when the equation y = f(x) is regarded as a functional relationship between dependent and independent variables y and x. Leibniz's notation makes this relationship explicit by writing the derivative as: [ 1 ] d y d x . {\displaystyle {\frac {dy}{dx}}.}
A difference equation is an equation where the unknown is a function f that occurs in the equation through f(x), f(x−1), ..., f(x−k), for some whole integer k called the order of the equation. If x is restricted to be an integer, a difference equation is the same as a recurrence relation
Note: If f takes its values in a ring (in particular for real or complex-valued f ), there is a risk of confusion, as f n could also stand for the n-fold product of f, e.g. f 2 (x) = f(x) · f(x). [11] For trigonometric functions, usually the latter is meant, at least for positive exponents. [11]
Cauchy's functional equation is the functional equation: (+) = + (). A function that solves this equation is called an additive function.Over the rational numbers, it can be shown using elementary algebra that there is a single family of solutions, namely : for any rational constant .
Every equation in the unknown may be rewritten as = by regrouping all the terms in the left-hand side. It follows that the solutions of such an equation are exactly the zeros of the function . In other words, a "zero of a function" is precisely a "solution of the equation obtained by equating the function to 0", and the study of zeros of ...