IMSL_ERF

Syntax | Return Value | Arguments | Keywords | Discussion | Examples | Version History

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

Note
This routine requires an IDL Advanced Math and Stats license. For more information, contact your ITT Visual Information Solutions sales or technical support representative.

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

If present and nonzero, double precision is used.

INVERSE

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

Discussion

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 Figure 12-1.

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

Figure 12-1: Plot of erf(x)

Example 2

Plot the inverse of the error function over ( –1, –1). The results are shown in Figure 12-2.

x = 2 * FINDGEN(100)/99 - 1 
PLOT, x, IMSL_ERF(x(1:98), /Inverse), XTitle = 'x', $ 
   YTitle = 'erf!E-1!N(x)' 

Figure 12-2: Plot of erf^–1(x)

Version History