large arrays and error virtual memory exhausted

[Joao Cardoso]

Hello,

I have the following error in octave-1.1.1  on a sco 3.2v4.0 with 
16Mbytes of memory and 20Mbytes of swap,

        "error: new: virtual memory exhausted -- stopping myself"

when working with large arrays (500x500 and greater).

It seems to me that the error "new: virtual memory exhausted" comes from gcc,
but I can't check it, as I have already removed the sources.

The strange thing is that virtual memory does not seem to be exhausted.
Voila a "sar -r" report:

05:01:45     257   25280
05:01:55     252   25280
05:02:05     245   24504
05:02:15     236   16280
05:02:25     307   16256
05:02:35     200   14080
05:02:45     169   14080
05:02:55     169   14080
05:03:05     169   14080
05:03:15     169   14080
05:03:25     169   14080
05:03:35     169   14080
05:03:45     169   14080
05:03:55     169   14080        <- octave has stopped itself
05:04:05    1272   26152
05:04:15    2119   26152

When creating large matrices, is it better, both in terms of memory 
allocation/fragmentation (and execution speed) to previously allocate 
a full matrix? what is the better way?

In a function is it wise to clear an unneeded variable? how? clear, clear -x ?

e.g.,

b = ones(size(a));      # is advantageous?
for i=1:rows(a)
        b(i,:) = foo(a(...
endfor
clear a;                # any advantage?

Thanks,

Joao Cardoso, address@hidden