C DLGA 10
C ..................................................................DLGA 20
C DLGA 30
C SUBROUTINE DLGAM DLGA 40
C DLGA 50
C PURPOSE DLGA 60
C COMPUTES THE DOUBLE PRECISION NATURAL LOGARITHM OF THE DLGA 70
C GAMMA FUNCTION OF A GIVEN DOUBLE PRECISION ARGUMENT. DLGA 80
C DLGA 90
C USAGE DLGA 100
C CALL DLGAM(XX,DLNG,IER) DLGA 110
C DLGA 120
C DESCRIPTION OF PARAMETERS DLGA 130
C XX - THE DOUBLE PRECISION ARGUMENT FOR THE LOG GAMMA DLGA 140
C FUNCTION. DLGA 150
C DLNG - THE RESULTANT DOUBLE PRECISION LOG GAMMA FUNCTION DLGA 160
C VALUE. DLGA 170
C IER - RESULTANT ERROR CODE WHERE DLGA 180
C IER= 0----NO ERROR. DLGA 190
C IER=-1----XX IS WITHIN 10**(-9) OF BEING ZERO OR XX DLGA 200
C IS NEGATIVE. DLNG IS SET TO -1.OD75. DLGA 210
C IER=+1----XX IS GREATER THAN 10**70. DLNG IS SET TO DLGA 220
C +1.OD75. DLGA 230
C DLGA 240
C REMARKS DLGA 250
C NONE DLGA 260
C DLGA 270
C SUBROUTINES AND FUNCTION SUBPROGRAMS REQUIRED DLGA 280
C NONE DLGA 290
C DLGA 300
C METHOD DLGA 310
C THE EULER-MCLAURIN EXPANSION TO THE SEVENTH DERIVATIVE TERM DLGA 320
C IS USED, AS GIVEN BY M. ABRAMOWITZ AND I.A. STEGUN, DLGA 330
C 'HANDBOOK OF MATHEMATICAL FUNCTIONS', U. S. DEPARTMENT OF DLGA 340
C COMMERCE, NATIONAL BUREAU OF STANDARDS APPLIED MATHEMATICS DLGA 350
C SERIES, 1966, EQUATION 6.1.41. DLGA 360
C DLGA 370
C ..................................................................DLGA 380
C DLGA 390
SUBROUTINE DLGAM(XX,DLNG,IER) DLGA 400
DOUBLE PRECISION XX,ZZ,TERM,RZ2,DLNG DLGA 410
IER=0 DLGA 420
ZZ=XX DLGA 430
IF(XX-1.D10) 2,2,1 DLGA 440
1 IF(XX-1.7D33) 8,9,9 DLGA 450
C DLGA 460
C SEE IF XX IS NEAR ZERO OR NEGATIVE DLGA 470
C DLGA 480
2 IF(XX-1.D-9) 3,3,4 DLGA 490
3 IER=-1 DLGA 500
DLNG=-1.7D38 DLGA 510
GO TO 10 DLGA 520
C DLGA 530
C XX GREATER THAN ZERO AND LESS THAN OR EQUAL TO 1.D+10 DLGA 540
C DLGA 550
4 TERM=1.D0 DLGA 560
5 IF(ZZ-18.D0) 6,6,7 DLGA 570
6 TERM=TERM*ZZ DLGA 580
ZZ=ZZ+1.D0 DLGA 590
GO TO 5 DLGA 600
7 RZ2=1.D0/ZZ**2 DLGA 610
DLNG =(ZZ-0.5D0)*DLOG(ZZ)-ZZ +0.9189385332046727 -DLOG(TERM)+ DLGA 620
1(1.D0/ZZ)*(.8333333333333333D-1 -(RZ2*(.2777777777777777D-2 +(RZ2*DLGA 630
2(.7936507936507936D-3 -(RZ2*(.5952380952380952D-3))))))) DLGA 640
GO TO 10 DLGA 650
C DLGA 660
C XX GREATER THAN 1.D+10 AND LESS THAN 1.D+70 DLGA 670
C DLGA 680
8 DLNG=ZZ*(DLOG(ZZ)-1.D0) DLGA 690
GO TO 10 DLGA 700
C DLGA 710
C XX GREATER THAN OR EQUAL TO 1.D+70 DLGA 720
C DLGA 730
9 IER=+1 DLGA 740
DLNG=1.7D38 DLGA 750
10 RETURN DLGA 760
END DLGA 770