SLATEC Routines --- QNG ---

*DECK QNG
      SUBROUTINE QNG (F, A, B, EPSABS, EPSREL, RESULT, ABSERR, NEVAL,
     +   IER)
C***BEGIN PROLOGUE  QNG
C***PURPOSE  The routine calculates an approximation result to a
C            given definite integral I = integral of F over (A,B),
C            hopefully satisfying following claim for accuracy
C            ABS(I-RESULT).LE.MAX(EPSABS,EPSREL*ABS(I)).
C***LIBRARY   SLATEC (QUADPACK)
C***CATEGORY  H2A1A1
C***TYPE      SINGLE PRECISION (QNG-S, DQNG-D)
C***KEYWORDS  AUTOMATIC INTEGRATOR, GAUSS-KRONROD(PATTERSON) RULES,
C             NONADAPTIVE, QUADPACK, QUADRATURE, SMOOTH INTEGRAND
C***AUTHOR  Piessens, Robert
C             Applied Mathematics and Programming Division
C             K. U. Leuven
C           de Doncker, Elise
C             Applied Mathematics and Programming Division
C             K. U. Leuven
C***DESCRIPTION
C
C NON-ADAPTIVE INTEGRATION
C STANDARD FORTRAN SUBROUTINE
C REAL VERSION
C
C           F      - Real version
C                    Function subprogram defining the integrand function
C                    F(X). The actual name for F needs to be declared
C                    E X T E R N A L in the driver program.
C
C           A      - Real version
C                    Lower limit of integration
C
C           B      - Real version
C                    Upper limit of integration
C
C           EPSABS - Real
C                    Absolute accuracy requested
C           EPSREL - Real
C                    Relative accuracy requested
C                    If  EPSABS.LE.0
C                    And EPSREL.LT.MAX(50*REL.MACH.ACC.,0.5D-28),
C                    The routine will end with IER = 6.
C
C         ON RETURN
C           RESULT - Real
C                    Approximation to the integral I
C                    Result is obtained by applying the 21-POINT
C                    GAUSS-KRONROD RULE (RES21) obtained by optimal
C                    addition of abscissae to the 10-POINT GAUSS RULE
C                    (RES10), or by applying the 43-POINT RULE (RES43)
C                    obtained by optimal addition of abscissae to the
C                    21-POINT GAUSS-KRONROD RULE, or by applying the
C                    87-POINT RULE (RES87) obtained by optimal addition
C                    of abscissae to the 43-POINT RULE.
C
C           ABSERR - Real
C                    Estimate of the modulus of the absolute error,
C                    which should EQUAL or EXCEED ABS(I-RESULT)
C
C           NEVAL  - Integer
C                    Number of integrand evaluations
C
C           IER    - IER = 0 normal and reliable termination of the
C                            routine. It is assumed that the requested
C                            accuracy has been achieved.
C                    IER.GT.0 Abnormal termination of the routine. It is
C                            assumed that the requested accuracy has
C                            not been achieved.
C           ERROR MESSAGES
C                    IER = 1 The maximum number of steps has been
C                            executed. The integral is probably too
C                            difficult to be calculated by DQNG.
C                        = 6 The input is invalid, because
C                            EPSABS.LE.0 AND
C                            EPSREL.LT.MAX(50*REL.MACH.ACC.,0.5D-28).
C                            RESULT, ABSERR and NEVAL are set to zero.
C
C***REFERENCES  (NONE)
C***ROUTINES CALLED  R1MACH, XERMSG
C***REVISION HISTORY  (YYMMDD)
C   800101  DATE WRITTEN
C   890531  Changed all specific intrinsics to generic.  (WRB)
C   890531  REVISION DATE from Version 3.2
C   891214  Prologue converted to Version 4.0 format.  (BAB)
C   900315  CALLs to XERROR changed to CALLs to XERMSG.  (THJ)
C***END PROLOGUE  QNG