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IMSL_ERF

IMSL_ERF

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



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


6.4
Introduced



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