On May 21, 7:49 pm, glen herrmannsfeldt
ugcs.caltech.edu> wrote:> John Harper wrote:
>
> (snip)
>
>> I have another problem with Wade's terminology. c is a velocity, which
>> happens to be a rational (for that matter an integer) number of metres
>> per second, which Paul gave. c is NOT a rational number. Rational
>> numbers are dimensionless. Remember the spacecraft that crashed on Mars
>> because someone was careless with units...
>
> I would agree with you, except that this is the Fortran newsgroup
> where variables do not have units. The quantity stored in the
> variable is the desired quantity divided by the appropriate units.
>
> It seems to me that physicists and related scientists tend to
> consider variables as holding a quantity with units, while
> engineers tend to consider the units as part of the equation.
>
> For the latter case, you might see in a book:
>
> F(Newtons) = m (kilograms) * a (meters/second**2).
program elliot7
implicit none
integer, parameter :: dp = kind(1.0d0)
real(kind=dp):: x,U0,E0,PIE, c, e0_calc
PIE = 4* atan(1.0)
U0=(1E-7_dp)*4.0 * PIE
E0= 8.854187E-12_dp
c = 2.99792458E8_dp
x = (E0*U0)**(-.5)
write (*,'(f30.20)') x, E0, U0, PIE
write (*, *) "going the other way"
e0_calc = 1/ (U0 * c**2.0)
write (*,'(f35.25)') c, U0, PIE, e0_calc
write (*,*) "12345678.0000000000012345678911234"
write (*,*) "12345678.1234567891123456789212345"
! end source begin output
end program elliot7
299792467.67059397698000000000
0.00000000000885418700
0.00000125663709640503
3.14159274101257324230
going the other way
299792458.0000000000000000000000000
0.0000012566370964050291944
3.1415927410125732423000000
0.0000000000088541875712302
12345678.0000000000012345678911234
12345678.1234567891123456789212345
This is the latest version of this program. I tried to get as much
width as I could for e0_calc. When I took E0 from a website that gave
it to 7 figures it gives the speed of light off by 9 m/s, which is
faster than Ben Johnson. I'd be curious to know how much accuracy I
got.
One question: If I have a variable declared as dp and assign it a
value like (1E-7)*4.0 , am I well-advised to append _dp on the things
on the RHS?
--
Wade Ward
