NAG CL Interface
s21bjc (ellipint_​complete_​2)

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1 Purpose

s21bjc returns a value of the classical (Legendre) form of the complete elliptic integral of the second kind.

2 Specification

#include <nag.h>
double  s21bjc (double dm, NagError *fail)
The function may be called by the names: s21bjc, nag_specfun_ellipint_complete_2 or nag_elliptic_integral_complete_e.

3 Description

s21bjc calculates an approximation to the integral
E(m) = 0 π2 (1-msin2θ) 12 dθ ,  
where m1 .
The integral is computed using the symmetrised elliptic integrals of Carlson (Carlson (1979) and Carlson (1988)). The relevant identity is
E(m) = RF (0,1-m,1) - 13 mRD (0,1-m,1) ,  
where RF is the Carlson symmetrised incomplete elliptic integral of the first kind (see s21bbc) and RD is the Carlson symmetrised incomplete elliptic integral of the second kind (see s21bcc).

4 References

NIST Digital Library of Mathematical Functions
Carlson B C (1979) Computing elliptic integrals by duplication Numerische Mathematik 33 1–16
Carlson B C (1988) A table of elliptic integrals of the third kind Math. Comput. 51 267–280

5 Arguments

1: dm double Input
On entry: the argument m of the function.
Constraint: dm1.0.
2: fail NagError * Input/Output
The NAG error argument (see Section 7 in the Introduction to the NAG Library CL Interface).

6 Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 3.1.2 in the Introduction to the NAG Library CL Interface for further information.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
See Section 7.5 in the Introduction to the NAG Library CL Interface for further information.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 8 in the Introduction to the NAG Library CL Interface for further information.
NE_REAL
On entry, dm=value; the integral is undefined.
Constraint: dm1.0.

7 Accuracy

In principle s21bjc is capable of producing full machine precision. However, round-off errors in internal arithmetic will result in slight loss of accuracy. This loss should never be excessive as the algorithm does not involve any significant amplification of round-off error. It is reasonable to assume that the result is accurate to within a small multiple of the machine precision.

8 Parallelism and Performance

Background information to multithreading can be found in the Multithreading documentation.
s21bjc is not threaded in any implementation.

9 Further Comments

You should consult the S Chapter Introduction, which shows the relationship between this function and the Carlson definitions of the elliptic integrals. In particular, the relationship between the argument-constraints for both forms becomes clear.
For more information on the algorithms used to compute RF and RD , see the function documents for s21bbc and s21bcc, respectively.

10 Example

This example simply generates a small set of nonextreme arguments that are used with the function to produce the table of results.

10.1 Program Text

Program Text (s21bjce.c)

10.2 Program Data

None.

10.3 Program Results

Program Results (s21bjce.r)