Calculating Members of the Fibonacci Series
Norman
Walsh
This trivial document describes a simple, recursive
implementation of the Fibonacci series in Perl. The principal
motivation for this document is to demonstrate the use of Literate XML.
Recursive Definition
The Fibonacci series begins: 1 1 2 3 5 8 13... Each member of
the series, after the first two, is the sum of the preceding two
members.
This can be implemented recursively by calculating the preceding
two members of the series and returning their sum:
&fib($n-2) + &fib($n-1);
The <function>fib</function> Function
The heart of this program is the recursive function that
calculates the members of the Fibonacci series.
The first and second members of the Fibonnacci series are
1
; all other values are calculated recursively.
sub fib {
my $n = shift;
if ($n <= 2) {
return 1;
} else {
return
}
}
Code Preamble
The program preamble simply establishes a default location for
the Perl executable and informs the interpreter that we want to use
the strict pragma.
#!/usr/bin/perl -w
use strict;
Argument Checking
This program expects its argument on the command line and it expects
that argument to be an unsigned decimal integer.
my $num = shift @ARGV || die;
die "Not a number: $num\n" if $num !~ /^\d+$/;
The Program
The program prints out the Fibonacci number requested:
print "Fib($num) = ", &fib($num), "\n";