Approximation error

In numerical analysis, approximation error is a measure of the difference between the exact value and an approximation.

The error of b as an approximation of a is:

${\displaystyle a-b\,\!.}$

The absolute error of b as an approximation of a is:

${\displaystyle |a-b|\,\!.}$

The relative error of b as an approximation of a is:

${\displaystyle {\frac {|a-b|}{|a|}}.}$