Domain and Range of FORTRAN Natural Log Functions (35872)
The information in this article applies to:
- Microsoft FORTRAN Compiler for MS-DOS 4.0
- Microsoft FORTRAN Compiler for MS-DOS 4.01
- Microsoft FORTRAN Compiler for MS-DOS 4.1
- Microsoft FORTRAN Compiler for MS-DOS 5.0
- Microsoft FORTRAN Compiler for MS-DOS 5.1
- Microsoft FORTRAN PowerStation for MS-DOS 1.0
- Microsoft FORTRAN PowerStation for MS-DOS 1.0a
- Microsoft Fortran Powerstation 32 for Windows NT 1.0
- Microsoft Fortran Powerstation 32 for Windows NT 4.0
This article was previously published under Q35872 SUMMARY
The program below demonstrates the use of the exp (e**n) and log
FORTRAN natural logarithm functions, using the limits of real*4 (or
real) and real*8 values. Both the domain and range of these functions
must be valid real*4 values for exp and log, and real*8 values for
dexp and dlog. Consequently, the highest acceptable argument to the
exp functions is the natural log of the maximum real number for the
respective floating-point precisions.
MORE INFORMATION
The following demonstrates this information:
c Program to manipulate natural log and exp functions with greatest and
c smallest real*4 and real*8 values. The 16th decimal digit displayed
c exceeds the 15 significant digits, and may not be accurate.
c Define extreme real*4 and real*8 values, and double- and
c single-precision "e"
real*8 maxr8, minr8, pos0r8, neg0r8, e8
real*4 maxr4, minr4, pos0r4, neg0r4, e4
maxr8 = 1.7976931348623156d+308
minr8 = -1.7976931348623156d+308
pos0r8 = 2.23d-308
neg0r8 = -2.23d-308
e8 = dexp(1)
maxr4 = 1.701411e+38
minr4 = -1.701411e+38
pos0r4 = 1.701411e-38
neg0r4 = -1.701411e-38
e4 = exp(1)
write(*,*)
write(*,*) 'Program to demonstrate use of natural log functions'
write(*,*) 'with domain & range values at floating point limits.'
write(*,*)
write(*,*) 'There are 7 significant decimal digits in a real*4'
write(*,*) '15 (or 16) significant decimal digits in a real*8.'
write(*,*)
write(*,*) 'The Intel coprocessor reference states that the'
write(*,*) 'range of double precision (real*8) values is'
write(*,*) 'approximately +/-2.23e-308 to +/-1.80e308. The'
write(*,*) 'larger real*8 has been carried out to additional'
write(*,*) 'digits of signifigance below.'
write(*,*)
write(*,*) 'Press ENTER to continue...'
read(*,*)
write(*,*)
write(*,*) 'Display extreme real*4 and real*8 values:'
write(*,*)
write(*,*) 'max real*8 = ', maxr8
write(*,*) 'min real*8 = ', minr8
write(*,*) 'smallest positive r8 = ', pos0r8
write(*,*) 'smallest negative r8 = ', neg0r8
write(*,*)
write(*,*) 'max real*4 = ', maxr4
write(*,*) 'min real*4 = ', minr4
write(*,*) 'smallest positive r4 = ', pos0r4
write(*,*) 'smallest negative r4 = ', neg0r4
write(*,*)
write(*,*) 'Press ENTER to continue...'
read(*,*)
write(*,*) 'Perform real*4 and real*8 natural log and'
write(*,*) 'exponentiation functions on limit values:'
write(*,*)
write(*,*) 'dexp(1) = real*8 e = ', e8
write(*,*) 'dlog(maxr8) = ', dlog(maxr8)
write(*,*) 'dexp(dlog(maxr8)) = ', dexp(dlog(maxr8))
write(*,*) 'dlog(smallest pos r8)= ', dlog(pos0r8)
write(*,*) 'dexp(minr8) = ', dexp(minr8)
write(*,*)
write(*,*) 'exp(1) = real*4 e = ', e4
write(*,*) 'log(maxr4) = ', log(maxr4)
write(*,*) 'exp(log(maxr4)) = ', exp(log(maxr4))
write(*,*) 'log(smallest pos r8) = ', log(pos0r4)
write(*,*) 'exp(minr4) = ', exp(minr4)
write(*,*)
write(*,*) 'Program completed. Good-bye.'
end
| Modification Type: | Major | Last Reviewed: | 12/1/2003 |
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| Keywords: | kbLangFortran KB35872 |
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