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First attempt at single precision tyeps * * * corrections to qrupdate single precision routines * * * prefer demotion to single over promotion to double * * * Add single precision support to log2 function * * * Trivial PROJECT file update * * * Cache optimized hermitian/transpose methods * * * Add tests for tranpose/hermitian and ChangeLog entry for new transpose code
author David Bateman <dbateman@free.fr>
date Sun, 27 Apr 2008 22:34:17 +0200
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1 *DECK R9LGIT
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2 FUNCTION R9LGIT (A, X, ALGAP1)
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3 C***BEGIN PROLOGUE R9LGIT
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4 C***SUBSIDIARY
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5 C***PURPOSE Compute the logarithm of Tricomi's incomplete Gamma
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6 C function with Perron's continued fraction for large X and
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7 C A .GE. X.
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8 C***LIBRARY SLATEC (FNLIB)
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9 C***CATEGORY C7E
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10 C***TYPE SINGLE PRECISION (R9LGIT-S, D9LGIT-D)
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11 C***KEYWORDS FNLIB, INCOMPLETE GAMMA FUNCTION, LOGARITHM,
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12 C PERRON'S CONTINUED FRACTION, SPECIAL FUNCTIONS, TRICOMI
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13 C***AUTHOR Fullerton, W., (LANL)
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14 C***DESCRIPTION
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15 C
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16 C Compute the log of Tricomi's incomplete gamma function with Perron's
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17 C continued fraction for large X and for A .GE. X.
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18 C
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19 C***REFERENCES (NONE)
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20 C***ROUTINES CALLED R1MACH, XERMSG
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21 C***REVISION HISTORY (YYMMDD)
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22 C 770701 DATE WRITTEN
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23 C 890531 Changed all specific intrinsics to generic. (WRB)
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24 C 890531 REVISION DATE from Version 3.2
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25 C 891214 Prologue converted to Version 4.0 format. (BAB)
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26 C 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ)
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27 C 900720 Routine changed from user-callable to subsidiary. (WRB)
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28 C***END PROLOGUE R9LGIT
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29 SAVE EPS, SQEPS
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30 DATA EPS, SQEPS / 2*0.0 /
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31 C***FIRST EXECUTABLE STATEMENT R9LGIT
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32 IF (EPS.EQ.0.0) EPS = 0.5*R1MACH(3)
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33 IF (SQEPS.EQ.0.0) SQEPS = SQRT(R1MACH(4))
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34 C
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35 IF (X .LE. 0.0 .OR. A .LT. X) CALL XERMSG ('SLATEC', 'R9LGIT',
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36 + 'X SHOULD BE GT 0.0 AND LE A', 2, 2)
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37 C
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38 AX = A + X
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39 A1X = AX + 1.0
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40 R = 0.0
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41 P = 1.0
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42 S = P
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43 DO 20 K=1,200
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44 FK = K
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45 T = (A+FK)*X*(1.0+R)
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46 R = T/((AX+FK)*(A1X+FK)-T)
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47 P = R*P
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48 S = S + P
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49 IF (ABS(P).LT.EPS*S) GO TO 30
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50 20 CONTINUE
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51 CALL XERMSG ('SLATEC', 'R9LGIT',
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52 + 'NO CONVERGENCE IN 200 TERMS OF CONTINUED FRACTION', 3, 2)
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53 C
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54 30 HSTAR = 1.0 - X*S/A1X
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55 IF (HSTAR .LT. SQEPS) CALL XERMSG ('SLATEC', 'R9LGIT',
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56 + 'RESULT LESS THAN HALF PRECISION', 1, 1)
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57 C
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58 R9LGIT = -X - ALGAP1 - LOG(HSTAR)
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59 C
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60 RETURN
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61 END