ELK
This function evaluates the complete elliptic integral of the kind K(x).
Function Return Value
ELK — Function value. (Output)
Required Arguments
X — Argument for which the function value is desired. (Input)
X must be greater than or equal to 0 and less than 1.
FORTRAN 90 Interface
Generic: ELK (X)
Specific: The specific interface names are S_ELK and D_ELK.
FORTRAN 77 Interface
Single: ELK (X)
Double: The double precision name is DELK.
Description
The complete elliptic integral of the first kind is defined to be
 
The argument x must satisfy 0   x < 1; otherwise, ELK is set to b = AMACH(2), the largest representable floating‑point number.
The function K(x) is computed using the routine ELRF and the relation K(x) = RF(0, 1  x, 1).
Figure 17, Plot of K(x) and E(x)
Example
In this example, K(0) is computed and printed.
 
USE ELK_INT
USE UMACH_INT
 
IMPLICIT NONE
! Declare variables
INTEGER NOUT
REAL VALUE, X
! Compute
X = 0.0
VALUE = ELK(X)
! Print the results
CALL UMACH (2, NOUT)
WRITE (NOUT,99999) X, VALUE
99999 FORMAT (' ELK(', F6.3, ') = ', F6.3)
END
Output
 
ELK( 0.000) = 1.571
Published date: 03/19/2020
Last modified date: 03/19/2020