8FUNCTIONS: irnum - CYANA function

Synopsis: irnum(<integer>) = <integer>

Given the external residue number that is used to identify the residue
in the input data files, this function returns the corresponding
residue index. The inverse function, 'rnum' is available, too.

The residues are indexed from 1 to nr according to the sequence
declared in the sequence file. Note that the (external) residue number
that is used to identify a residue in the input files can be different
from the (internal) residue index.
