file size

[Zdenko Tomasic]

In article <1190 at unisoft.UUCP> john at unisoft.UUCP (John Sovereign) writes:
>
>A/UX inherits support for file size limits from System V,
>which provides a ulimit(2) system call that allows a process
>to query and set its file size limit (among other things).
>The ulimit(2) file size is defined in 512-byte blocks and
>may only be increased if you're root.
>
>The default limit in A/UX is equivalent to 8 GB, which exceeds
>the size which you may actually create since the file offset is
>an unsigned long (32-bits).
>
   Thanks for the info!

>Let me know if you ever create a 2 GB file. :->
                                  ^^^^
>
Let's see: 
In quantum chemistry calculations, in order to calculate electronic
energy (including electron correlation) of a substance, one needs
roughly N**4/8 integrals. N is a size of a basis functions used in
integral calculation. If one sticks to not-so-big 4-31G basis set
which includes 2 functions for hydrogen (H) and 9 for carbon (C),
oxygen (O) and nitrogen (N) each, the ordinary CHOLESTEROL molecule
(C27H46O) will require N of 344 (=27*9+46*2+9) basis functions. In
that case there are 1 750 426 112 integrals which in double precision
(with 8 bytes per integral) means a file of 14 003 408 896 bytes,
i.e.  more than 14 GB.
                ^^^^^

Of course, one would not try that on Mac, but maybe (or maybe not even
there!) Cray or ETA-10 .
You see, such big files are not all that unusual, not to mention
real big bio-molecules (hundreds, thousands of atoms).
They are naturally out of reach for serious calculations with present
resources.

>John Sovereign
>UniSoft Corporation
>uunet!unisoft!john
>#include <disclaimer.h>



Zdenko Tomasic
UWM, Chem. Dept.
Milwaukee,WI,53201
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