From help-octave-request at bevo dot che dot wisc dot edu Thu Jan  8 20:50:58 2004
Subject: Ops on matrix in cell array much slower than on bare matrix
From: Glenn Golden <gdg at zplane dot com>
To: help-octave at bevo dot che dot wisc dot edu
Date: Thu, 08 Jan 2004 19:49:18 -0700

Any ideas on this?  It's eating my lunch, and the workaround is very
ugly.  See comments in script.

Octave version = 2.1.50.

Thanks,

Glenn Golden


===== begin example script =====

ysize = 100000;
nloops = 1000;

#
# Loop to evaluate execution time of assignment of a scalar to a matrix
# element.  On my machine, with parameters above, execution time per
# assignment is around 20 usec.
#
Y = zeros(ysize,1);
start = cputime();
for k = 1:nloops
    Y(1) = 123.4;
endfor
et = cputime() - start;
fprintf(stderr, "et/assignment = %f\n", et/nloops);


#
# Same thing as above, except using cell array to hold the matrix. Average
# execution time per assignment is around 100 times larger (2.3 ms) than
# above.  The slowdown factor is related to the size of the matrix (ysize). 
# 
y = cell(1,2);
y{1} = zeros(ysize,1);
start = cputime();
for k = 1:nloops
    y{1}(1) = 123.4;   
endfor
et = cputime() - start;
fprintf(stderr, "et/assignment = %f\n", et/nloops);

===== end example script =====



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