ERFCI
This function evaluates the inverse complementary error function.
Function Return Value
ERFCI — Function value. (Output)
Required Arguments
X — Argument for which the function value is desired. (Input)
FORTRAN 90 Interface
Generic: ERFCI (X)
Specific: The specific interface names are S_ERFCI and D_ERFCI.
FORTRAN 77 Interface
Single: ERFCI (X)
Double: The double precision function name is DERFCI.
Description
The function ERFCI(X) computes the inverse of the complementary error function erfc x, defined in ERFC.
The function ERFCI(X) is defined for 0 < x < 2. If xmax < x < 2, then the answer will be less accurate than half precision. Very approximately,
Where ɛ = AMACH(4) is the machine precision.
Figure 10, Plot of erf‑1(x)
Comments
Informational Error
Type | Code | Description |
|---|---|---|
3 | 2 | Result of ERFCI(X) is accurate to less than one‑half precision because the argument is too close to 2.0. |
Example
In this example, erfc‑1(erfc(1.0)) is computed and printed.
USE ERFCI_INT
USE ERFC_INT
USE UMACH_INT
IMPLICIT NONE
! Declare variables
INTEGER NOUT
REAL VALUE, X
! Compute
X = ERFC(1.0)
VALUE = ERFCI(X)
! Print the results
CALL UMACH (2, NOUT)
WRITE (NOUT,99999) X, VALUE
99999 FORMAT (' ERFCI(', F6.3, ') = ', F6.3)
END
Output
ERFCI( 0.157) = 1.000
