## What is the Error Function?

The **error function** (erf) is a special function which gets its name for its importance in the study of errors. It is sometimes called the *Gauss *or *Gaussian Error Function* and occasionally a *Cramp function.*

As well as error theory, the error function is also used in probability theory, mathematical physics (where it can be expressed as a special case of the Whittaker function), and a wide variety of other theoretical and practical applications. For example, Fresnel integrals, which are derived from the error function, are used in the theory of optics.

In probability and statistics, the function integrates the normal distribution (aka Gaussian Distribution). It gives the probability that a normally distributed random variable Y (with mean 0 and variance ½), falls into the range [−x, x].

## Formula and Properties

The error function is defined by the following integral:

The function has the following four properties:

- erf (-∞) = -1
- erf (+∞) = 1
- erf (-x) = -erf (x)
- erf (x*) = [erf (x)]*

(* is a complex conjugate, where the real and imaginary parts are equal in magnitude but opposite in sign. For example, a + bi → a – bi)

## Graph of the Error Function

The error function is an odd function, which means it is symmetric about the origin.

## Table of Values

For a full list of the table of values, download this pdf (from Washington State University).

## Approximation for Erf

If you have a programmable calculator, the following formula which serves as a good approximation to the function. It’s accurate to 1 part in 10^{7} (Cheung, n.d.).

**erf(z) = 1 – (a _{1} T + a_{2} T^{2} + a_{3} T^{3} + a_{4} T^{4} + a_{5} T^{5} )**

) e^{-z2}

Where:

- T = 1 / (1 + (0.3275911 * z)),
- Z = a z-score
- a
_{1}= 0.254829592 - a
_{2}= -0.284496736 - a
_{3}= 1.421413741 - a
_{4}= -1.453152027 - a
_{4}= 1.061405429

## References

Andrews, L. (1998). Special Functions of Mathematics for Engineers. SPIE Press. Retrieved November 27, 2019 from: https://books.google.com/books?id=2CAqsF-RebgC

Cheung. Properties of … erf(z) And … erfc(z). Retrieved November 27, 2019 from: http://www.sci.utah.edu/~jmk/papers/ERF01.pdf

Lehtinen, N. (2010). Error Functions. Retrieved November 27, 2019 from: http://nlpc.stanford.edu/nleht/Science/reference/errorfun.pdf

Washington State University. Error Function. Retrieved November 27, 2019 from: http://courses.washington.edu/overney/privateChemE530/Handouts/Error%20Function.pdf

**CITE THIS AS:**

**Stephanie Glen**. "Error Function: Simple Definition, Table of Values" From

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