Rectangular function


The rectangular function is defined as
Alternative definitions of the function define to be 0, 1, or undefined.

Relation to the boxcar function

The rectangular function is a special case of the more general boxcar function:
where is the Heaviside function; the function is centered at and has duration, from to.

Fourier transform of the rectangular function

The unitary Fourier transforms of the rectangular function are
using ordinary frequency f, and
using angular frequency ω, where sinc function| is the unnormalized form of the sinc function.
Note that as long as the definition of the pulse function is only motivated by its behavior in the time-domain experience, there is no reason to believe that the oscillatory interpretation should be intuitive, or directly understood by humans. However, some aspects of the theoretical result may be understood intuitively, as finiteness in time domain corresponds to an infinite frequency response.

Relation to the triangular function

We can define the triangular function as the convolution of two rectangular functions:

Use in probability

Viewing the rectangular function as a probability density function, it is a special case of the continuous uniform distribution with. The characteristic function is
and its moment-generating function is
where is the hyperbolic sine function.

Rational approximation

The pulse function may also be expressed as a limit of a rational function:

Demonstration of validity

First, we consider the case where. Notice that the term is always positive for integer. However, and hence approaches zero for large.
It follows that:
Second, we consider the case where. Notice that the term is always positive for integer. However, and hence grows very large for large.
It follows that:
Third, we consider the case where. We may simply substitute in our equation:
We see that it satisfies the definition of the pulse function.