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C $Header: /u/gcmpack/models/MITgcmUV/eesupp/src/different_multiple.F,v 1.1 1998/05/21 18:30:08 cnh Exp $ |
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#include "CPP_EEOPTIONS.h" |
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CStartofinterface |
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LOGICAL FUNCTION DIFFERENT_MULTIPLE( freq, val1, val2 ) |
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C /==========================================================\ |
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C | LOGICAL FUNCTION DIFFERENT_MULTIPLE | |
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C | o Checks two numbers multiple of a third number. | |
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C |==========================================================| |
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C | This routine is used for diagnostic and other periodic | |
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C | operations. It is very sensitive to arithmetic precision.| |
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C | For IEEE conforming arithmetic is works well but for | |
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C | cases where short cut arithmetic is used it may not work| |
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C | as expected. To overcome this issue compile this routine | |
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C | separately with no optimisation. | |
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C \==========================================================/ |
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IMPLICIT NONE |
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C Returns TRUE if val1 and val2 are different multiples of freq. |
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cnh |
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_RL freq, val1, val2 |
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cnh |
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CEndofinterface |
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cnh |
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_RL f, v1, v2, v3, v4, d1, d2, d3, step |
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C o Do easy cases first. |
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DIFFERENT_MULTIPLE = .FALSE. |
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IF ( freq .EQ. 0. ) RETURN |
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IF ( ABS(val1-val2) .GT. freq ) THEN |
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DIFFERENT_MULTIPLE = .TRUE. |
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RETURN |
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ENDIF |
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cnh |
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C o This case is more complex because of round-off error |
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f = freq |
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v1 = val1 |
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v2 = val2 |
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step = v1-v2 |
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C Test v1 to see if its a "closest multiple" |
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v3 = v1 + step |
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v4 = NINT(v1/f)*f |
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d1 = v1-v4 |
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d2 = v2-v4 |
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d3 = v3-v4 |
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IF ( ABS(d1) .LE. ABS(d2) .AND. |
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& ABS(d1) .LE. ABS(d3) ) DIFFERENT_MULTIPLE = .TRUE. |
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cnh |
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cnh |
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END |