The IMSL_ERF function evaluates the real error function erf (x). Using a keyword, the inverse error function erf –1(x) can be evaluated.

The error function erf(x) is defined below:

All values of x are legal. The inverse error function y = erf –1(x) is such that x = erf (y).

## Examples

### Example 1

Plot the error function over [ –3, 3 ]. The results are shown in the figure that follows.

`x = 6 * FINDGEN(100)/99 - 3`
`PLOT, x, IMSL_ERF(x), XTitle = 'x', YTitle = 'erf(x)'`

### Example 2

Plot the inverse of the error function over ( –1, –1). The results are shown in the next figure.

.

x = 2 * FINDGEN(100)/99 - 1

PLOT, x, IMSL_ERF(x(1:98), /Inverse), XTitle = 'x', \$ YTitle = 'erf!E-1!N(x)'

## Syntax

Result = IMSL_ERF(X [, /DOUBLE] [, /INVERSE]

## Return Value

The value of the error function erf(x).

## Arguments

### X

Expression for which the error function is to be evaluated.

## Keywords

### DOUBLE (optional)

If present and nonzero, double precision is used.

### INVERSE (optional)

Evaluates the real inverse error function erf–1(x). The inverse error function is defined only for –1 < x < 1.

## Version History

 6.4 Introduced