ERFI
This function evaluates the inverse error function.
Function Return Value
ERFI — Function value. (Output)
Required Arguments
X — Argument for which the function value is desired. (Input)
FORTRAN 90 Interface
Generic: ERFI (X)
Specific: The specific interface names are S_ERFI and D_ERFI.
FORTRAN 77 Interface
Single: ERFI (X)
Double: The double precision function name is DERFI.
Description
The function ERFI(X) is defined for ∣x∣ < 1. If xmax< ∣x∣ < 1, then the answer will be less accurate than half precision. Very approximately,
where ɛ = AMACH(4) is the machine precision.
Figure 9, Plot of erf‑1(x)
Comments
Informational Error
Type | Code | Description |
|---|---|---|
3 | 2 | Result of ERFI(X) is accurate to less than one‑half precision because the absolute value of the argument is too large . |
Example
In this example, erf‑1(erf(1.0)) is computed and printed.
USE ERFI_INT
USE ERF_INT
USE UMACH_INT
IMPLICIT NONE
! Declare variables
INTEGER NOUT
REAL VALUE, X
! Compute
X = ERF(1.0)
VALUE = ERFI(X)
! Print the results
CALL UMACH (2, NOUT)
WRITE (NOUT,99999) X, VALUE
99999 FORMAT (' ERFI(', F6.3, ') = ', F6.3)
END
Output
ERFI( 0.843) = 1.000
