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SUBROUTINE DCEL2

PURPOSE
   COMPUTES THE GENERALIZED COMPLETE ELLIPTIC INTEGRAL OF
   SECOND KIND.

USAGE
   CALL DCEL2(RES,AK,A,B,IER)

DESCRIPTION OF PARAMETERS
   RES	 - RESULT VALUE IN DOUBLE PRECISION
   AK	 - MODULUS (INPUT) IN DOUBLE PRECISION
   A	 - DOUBLE PRECISION CONSTANT TERM IN NUMERATOR
   B	 - DOUBLE PRECISION FACTOR OF QUADRATIC TERM
	   IN NUMERATOR
   IER	 - RESULTANT ERROR CODE WHERE
	   IER=0  NO ERROR
	   IER=1  AK NOT IN RANGE -1 TO +1

REMARKS
   FOR ABS(AK) GE 1 THE RESULT IS SET TO 1.E75 IF B IS
   POSITIVE, TO -1.D75 IF B IS NEGATIVE.
   SPECIAL CASES ARE
   K(K) OBTAINED WITH A = 1, B = 1
   E(K) OBTAINED WITH A = 1, B = CK*CK WHERE CK IS
   COMPLEMENTARY MODULUS.
   B(K) OBTAINED WITH A = 1, B = 0
   D(K) OBTAINED WITH A = 0, B = 1
   WHERE K, E, B, D DEFINE SPECIAL CASES OF THE GENERALIZED
   COMPLETE ELLIPTIC INTEGRAL OF SECOND KIND IN THE USUAL
   NOTATION, AND THE ARGUMENT K OF THESE FUNCTIONS MEANS
   THE MODULUS.

SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED
   NONE

METHOD
   DEFINITION
   RES=INTEGRAL((A+B*T*T)/(SQRT((1+T*T)*(1+(CK*T)**2))*(1+T*T))
   SUMMED OVER T FROM 0 TO INFINITY).
   EVALUATION
   LANDENS TRANSFORMATION IS USED FOR CALCULATION.
   REFERENCE
   R.BULIRSCH, 'NUMERICAL CALCULATION OF ELLIPTIC INTEGRALS
   AND ELLIPTIC FUNCTIONS', HANDBOOK SERIES SPECIAL FUNCTIONS,
   NUMERISCHE MATHEMATIK VOL. 7, 1965, PP. 78-90.