From owner-help-octave at bevo dot che dot wisc dot edu  Wed Jan 17 04:01:25 1996
Subject: Aliasing (?) built-in functions
From: Ted dot Harding at nessie dot mcc dot ac dot uk (Ted Harding)
To: help-octave at bevo dot che dot wisc dot edu
Date: Wed, 17 Jan 1996 09:32:08 +0000 (GMT)

Hi Folks,

A report on a "feature" of octave which could set a trap for the unwary.
The following is artificial, to highlight the process.

Take an octave built-in function, such as "lgamma".

Write a function m-file, say "temp.m":

temp.m
------
function y = lgamma(x)
y=1;
endfunction

In octave, invoke it:--
octave:1> exp(temp(5))
warning: function name `lgamma' does not agree with function file name `temp.m'
error: can't redefine read-only function `temp'
error: `temp' undefined near line 1 column 5
error: evaluating index expression near line 1, column 5
error: evaluating argument list element number 0
error: evaluating index expression near line 1, column 1
octave:2>

So far so good. Now do it again:--
octave:4> exp(temp(5))
ans = 24.000
octave:5>

What seems to have happened is that "lgamma" has now been renamed "temp";
it seems "lgamma" can no longer be found:--
octave:5> exp(lgamma(5))
error: `lgamma' undefined near line 5 column 5
error: evaluating index expression near line 5, column 5
error: evaluating argument list element number 0
error: evaluating index expression near line 5, column 1
octave:6>

and this situation persists until you "quit" octave.

(For the curious: this was found when one of my student's wrote a program
called "lgamma" for matlab -- which doesn't have lgamma built in -- which
in fact computed the log-factorial, in a file which he finally renamed to
"lfact.m" without changing the contents of the file. When I ran his
program in octave the above was observed.)

Best wishes to all,
Ted.                                    (Ted dot Harding at nessie dot mcc dot ac dot uk)