<mathematics, algorithm> A mathematical procedure which
estimates values of a function for certain desired inputs
given values for known inputs.

If the desired input is outside the range of the known values
this is called extrapolation, if it is inside then it is
called interpolation.

The method works by fitting a "curve" (i.e. a function) to two
or more given points and then applying this function to the
required input. Example uses are calculating trigonometric
functions from tables and audio waveform sythesis.

The simplest form of interpolation is where a function, f(x),
is estimated by drawing a straight line ("linear
interpolation") between the nearest given points on either
side of the required input value:

f(x) ~ f(x1) + (f(x2) - f(x1))(x-x1)/(x2 - x1)

There are many variations using more than two points or higher
degree polynomial functions. The technique can also be
extended to functions of more than one input.