Chapter 9: Elliptic Integrals

ELE

This function evaluates the complete elliptic integral of the second kind E(x).

Function Return Value

ELE — 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 or equal to 1.

FORTRAN 90 Interface

Generic:                              ELE (X)

Specific:                             The specific interface names are S_ELE and D_ELE.

FORTRAN 77 Interface

Single:                                ELE (X)

Double:                              The double precision name is DELE.

Description

The complete elliptic integral of the second kind is defined to be

The argument x must satisfy 0 ≤ x < 1; otherwise, ELE is set to b = AMACH(2), the largest representable floating-point number.

The function E(x) is computed using the routines ELRF and ELRD. The computation is done using the relation

For a plot of E(x), see Figure 9- 1.

Example

In this example, E(0.33) is computed and printed.

 

      USE ELE_INT

      USE UMACH_INT

 

      IMPLICIT   NONE

!                                 Declare variables

      INTEGER    NOUT

      REAL       VALUE, X

!                                 Compute

      X     = 0.33

      VALUE = ELE(X)

!                                 Print the results

      CALL UMACH (2, NOUT)

      WRITE (NOUT,99999) X, VALUE

99999 FORMAT (' ELE(', F6.3, ') = ', F6.3)

      END

Output

 

ELE( 0.330) = 1.432



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