"Fossies" - the Fresh Open Source Software Archive  

Source code changes of the file "Basic/Pod/MATLAB.pod" between
PDL-2.074.tar.gz and PDL-2.075.tar.gz

About: PDL (Perl Data Language) aims to turn perl into an efficient numerical language for scientific computing (similar to IDL and MatLab).

MATLAB.pod  (PDL-2.074)	:	MATLAB.pod  (PDL-2.075)
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If you are a MATLAB user, this page is for you. It explains the key		If you are a MATLAB user, this page is for you. It explains the key
differences between MATLAB and PDL to help you get going as quickly		differences between MATLAB and PDL to help you get going as quickly
as possible.		as possible.
B<This document is not a tutorial>. For that, go to L<PDL::QuickStart|		B<This document is not a tutorial>. For that, go to L<PDL::QuickStart|
PDL::QuickStart>. This document B<complements> the Quick Start guide, as		PDL::QuickStart>. This document B<complements> the Quick Start guide, as
it highlights the key differences between MATLAB and PDL.		it highlights the key differences between MATLAB and PDL.
=head1 Perl		=head1 Perl
The key differences between MATLAB and PDL are threading, and B<Perl>.		The key differences between MATLAB and PDL are broadcasting, and B<Perl>.
Threading means you can get a reference to just a part of your data,		Broadcasting means you can get a reference to just a part of your data,
and operate on it in a way that makes sense for your application. Those		and operate on it in a way that makes sense for your application. Those
operations will be reflected in the original data.		operations will be reflected in the original data.
Perl is a general purpose programming language with thousands of modules		Perl is a general purpose programming language with thousands of modules
freely available on the web. PDL is an extension of Perl. This gives PDL		freely available on the web. PDL is an extension of Perl. This gives PDL
programs access to more features than most numerical tools can dream of.		programs access to more features than most numerical tools can dream of.
At the same time, most syntax differences between MATLAB and PDL are a		At the same time, most syntax differences between MATLAB and PDL are a
result of its Perl foundation.		result of its Perl foundation.
B<You do not have to learn much Perl to be effective with PDL>. But		B<You do not have to learn much Perl to be effective with PDL>. But
skipping to change at line 493		skipping to change at line 493
endfor }		endfor }
=over 5		=over 5
=item B<Note>		=item B<Note>
Never use for-loops for numerical work. Perl's for-loops are faster		Never use for-loops for numerical work. Perl's for-loops are faster
than MATLAB's, but they both pale against a "vectorized" operation.		than MATLAB's, but they both pale against a "vectorized" operation.
PDL has many tools that facilitate writing vectorized programs.		PDL has many tools that facilitate writing vectorized programs.
These are beyond the scope of this guide. To learn more, see:		These are beyond the scope of this guide. To learn more, see:
L<PDL::Indexing>, L<PDL::Threading>,		L<PDL::Indexing>, L<PDL::Broadcasting>,
and L<PDL::PP>.		and L<PDL::PP>.
Likewise, never use C<1..10> for numerical work, even outside a for-loop.		Likewise, never use C<1..10> for numerical work, even outside a for-loop.
C<1..10> is a Perl array. Perl arrays are designed for flexibility, not		C<1..10> is a Perl array. Perl arrays are designed for flexibility, not
speed. Use I<ndarrays> instead. To learn more, see the next section.		speed. Use I<ndarrays> instead. To learn more, see the next section.
=back		=back
=head2 ndarrays vs Perl Arrays		=head2 ndarrays vs Perl Arrays
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=over 5		=over 5
=item L<PDL::Indexing>		=item L<PDL::Indexing>
B<Level>: Beginner		B<Level>: Beginner
This beginner tutorial covers the standard "vectorization" feature that		This beginner tutorial covers the standard "vectorization" feature that
you already know from MATLAB. Use this page to learn how to avoid for-loops		you already know from MATLAB. Use this page to learn how to avoid for-loops
to make your program more efficient.		to make your program more efficient.
=item L<PDL::Threading>		=item L<PDL::Broadcasting>
B<Level>: Intermediate		B<Level>: Intermediate
PDL's "vectorization" feature goes beyond what most numerical software		PDL's "vectorization" feature goes beyond what most numerical software
can do. In this tutorial you'll learn how to "thread" over higher dimensions,		can do. In this tutorial you'll learn how to "broadcast" over higher dimensions,
allowing you to vectorize your program further than is possible in MATLAB.		allowing you to vectorize your program further than is possible in MATLAB.
=item Benchmarks		=item Benchmarks
B<Level>: Intermediate		B<Level>: Intermediate
Perl comes with an easy to use benchmarks module to help you find how		Perl comes with an easy to use benchmarks module to help you find how
long it takes to execute different parts of your code. It is a great		long it takes to execute different parts of your code. It is a great
tool to help you focus your optimization efforts. You can read about it		tool to help you focus your optimization efforts. You can read about it
online (L<http://perldoc.perl.org/Benchmark.html>) or through the		online (L<http://perldoc.perl.org/Benchmark.html>) or through the
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for v = 1:n; P(v, v) = v; end		for v = 1:n; P(v, v) = v; end
for k = 1:n		for k = 1:n
prevD = D;		prevD = D;
D = min(D,D(:,k) + D(k,:));		D = min(D,D(:,k) + D(k,:));
coords = find(D<prevD);		coords = find(D<prevD);
from_coords = n * (k-1) + mod(coords-1, n) + 1; % change col to k in 1-bas ed		from_coords = n * (k-1) + mod(coords-1, n) + 1; % change col to k in 1-bas ed
P(coords) = P(from_coords);		P(coords) = P(from_coords);
end		end
end		end
By comparison, the lack of "threading" means that to update the diagonal		By comparison, the lack of "broadcasting" means that to update the diagonal
requires a for-loop, which in the sphere of vectorised calculations is		requires a for-loop, which in the sphere of vectorised calculations is
a bad thing. The calculations of coordinates are complicated by the		a bad thing. The calculations of coordinates are complicated by the
1-based counting.		1-based counting.
=head1 COPYRIGHT		=head1 COPYRIGHT
Copyright 2010 Daniel Carrera (dcarrera@gmail.com). You can distribute and/or		Copyright 2010 Daniel Carrera (dcarrera@gmail.com). You can distribute and/or
modify this document under the same terms as the current Perl license.		modify this document under the same terms as the current Perl license.
See: L<http://dev.perl.org/licenses/>		See: L<http://dev.perl.org/licenses/>
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