d4/d50/r9lgit_8f_source.html

 *DECK R9LGIT

       FUNCTION r9lgit (A, X, ALGAP1)

 C***BEGIN PROLOGUE  R9LGIT

 C***SUBSIDIARY

 C***PURPOSE  Compute the logarithm of Tricomi's incomplete Gamma

 C            function with Perron's continued fraction for large X and

 C            A .GE. X.

 C***LIBRARY   SLATEC (FNLIB)

 C***CATEGORY  C7E

 C***TYPE      SINGLE PRECISION (R9LGIT-S, D9LGIT-D)

 C***KEYWORDS  FNLIB, INCOMPLETE GAMMA FUNCTION, LOGARITHM,

 C             PERRON'S CONTINUED FRACTION, SPECIAL FUNCTIONS, TRICOMI

 C***AUTHOR  Fullerton, W., (LANL)

 C***DESCRIPTION

 C

 C Compute the log of Tricomi's incomplete gamma function with Perron's

 C continued fraction for large X and for A .GE. X.

 C

 C***REFERENCES  (NONE)

 C***ROUTINES CALLED  R1MACH, XERMSG

 C***REVISION HISTORY  (YYMMDD)

 C   770701  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   900720  Routine changed from user-callable to subsidiary.  (WRB)

 C***END PROLOGUE  R9LGIT

       SAVE eps, sqeps

       DATA eps, sqeps / 2*0.0 /

 C***FIRST EXECUTABLE STATEMENT  R9LGIT

       IF (eps.EQ.0.0) eps = 0.5*r1mach(3)

       IF (sqeps.EQ.0.0) sqeps = sqrt(r1mach(4))

 C

       IF (x .LE. 0.0 .OR. a .LT. x) CALL xermsg('SLATEC', 'R9LGIT',

      +   'X SHOULD BE GT 0.0 AND LE A', 2, 2)

 C

       ax = a + x

       a1x = ax + 1.0

       r = 0.0

       p = 1.0

       s = p

       DO 20 k=1,200

         fk = k

         t = (a+fk)*x*(1.0+r)

         r = t/((ax+fk)*(a1x+fk)-t)

         p = r*p

         s = s + p

         IF (abs(p).LT.eps*s) go to 30

  20   CONTINUE

       CALL xermsg('SLATEC', 'R9LGIT',

      +   'NO CONVERGENCE IN 200 TERMS OF CONTINUED FRACTION', 3, 2)

 C

  30   hstar = 1.0 - x*s/a1x

       IF (hstar .LT. sqeps) CALL xermsg('SLATEC', 'R9LGIT',

      +   'RESULT LESS THAN HALF PRECISION', 1, 1)

 C

       r9lgit = -x - algap1 - log(hstar)

 C

       RETURN

       END

r9lgit
function r9lgit(A, X, ALGAP1)
Definition: r9lgit.f:2

log
OCTAVE_EXPORT octave_value_list or N dimensional array whose elements are all equal to the base of natural logarithms The constant ex $e satisfies the equation log(e)

to
may be zero for pure relative error test tem the relative tolerance must be greater than or equal to
Definition: Quad-opts.cc:233

xermsg
subroutine xermsg(LIBRAR, SUBROU, MESSG, NERR, LEVEL)
Definition: xermsg.f:2

abs
OCTAVE_EXPORT octave_value_list return the value of the option it must match the dimension of the state and the relative tolerance must also be a vector of the same length tem it must match the dimension of the state and the absolute tolerance must also be a vector of the same length The local error test applied at each integration step is xample roup abs(local error in x(i))<

octave_value::sqrt
octave_value sqrt(void) const
Definition: ov.h:1388