Nicolas ROUX wrote: > Hi, > > I need help ;-) > I have here a testcase which works much faster in Matlab than Numpy. > > The following code takes less than 0.9sec in Matlab, but 21sec in Python. > Numpy is 24 times slower than Matlab ! > The big trouble I have is a large team of people within my company is ready > to replace Matlab by Numpy/Scipy/Matplotlib, > but I have to demonstrate that this kind of Python Code is executed with the > same performance than Matlab, without writing C extension. > This is becoming a critical point for us. > > This is a testcase that people would like to see working without any code > restructuring. > The reasons are: > - this way of writing is fairly natural. > - the original code which showed me the matlab/Numpy performance differences > is much more complex, > and can't benefit from broadcasting or other numpy tips (I can later give > this code) > > ...So I really need to use the code below, without restructuring. > > Numpy/Python code: > ##################################################################### > import numpy > import time > > print "Start test \n" > > dim = 3000 > > a = numpy.zeros((dim,dim,3)) > > start = time.clock() > > for i in range(dim): > for j in range(dim): > a[i,j,0] = a[i,j,1] > a[i,j,2] = a[i,j,0] > a[i,j,1] = a[i,j,2] > > end = time.clock() - start > > print "Test done, %f sec" % end > ##################################################################### > > Matlab code: > ##################################################################### > 'Start test' > dim = 3000; > tic; > a =zeros(dim,dim,3); > for i = 1:dim > for j = 1:dim > a(i,j,1) = a(i,j,2); > a(i,j,2) = a(i,j,1); > a(i,j,3) = a(i,j,3); > end > end > toc > 'Test done' > ##################################################################### > > Any idea on it ? > Did I missed something ? >
I think on recent versions of matlab, there is nothing you can do without modifying the code: matlab has some JIT compilation for loops, which is supposed to speed up those cases - at least, that's what is claimed by matlab. The above loops are typical examples where this should work reasonably well I believe: http://www.mathworks.com/access/helpdesk_r13/help/techdoc/matlab_prog/ch7_pe10.html If you really have to use loops, then matlab will be faster. But maybe you don't; can you show us a more typical example ? cheers, David _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
