From pdl

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 as possible.

This document is not a tutorial. For that, go to the PDL Quick Start guide. This document complements the Quick Start guide, as it highlights the differences between MATLAB and PDL.

Contents 1 Perl 2 Language Syntax 2.1 Arrays and Matrices 2.2 Matrix Operations 2.3 Mathematical Functions 2.4 Matrix dimensions 2.5 Conditionals 3 List of Matlab functions grouped 3.1 Desktop Tools and Development Environment 3.2 Data Import and Export 3.3 Mathematics 3.4 Data Analysis 3.5 Programming and Data Types 3.6 Object-Oriented Programming 3.7 Graphics 3.8 3-D Visualization 3.9 GUI Development 3.10 External Interfaces 3.11 in ABC order 3.12 Other terms 3.13 Toolbox 3.13.1 Database Connectivity and Reporting

Perl

The key difference between MATLAB and PDL is PERL.

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 programs access to more features than most numerical tools can dream of.

Perl itself has excellent documentation at http://perldoc.perl.org. Or use the command perldoc perl.

To search through Perl modules, go to http://www.cpan.org

Language Syntax

Arrays and Matrices

Like MATLAB, PDL is an array-based numerical programming language. This section covers the basic array syntax.

The shell

Run the perldl command to start the PDL interactive shell.

Variables

In Perl, variables always start with the '$' sign.

 value  = 42      MATLAB
 $value = 42      PDL

Array

Use the "pdl" constructor to create a new PDL object.

 v  = [1,2,3,4]      MATLAB
 $v = pdl [1,2,3,4]  PDL

Matrix

 A  =      [ 1,2,3  ;  3,4,5 ]   MATLAB
 $A = pdl [ [1,2,3] , [3,4,5] ]  PDL

Display a matrix

 disp(A)   MATLAB
 
 print $A  PDL
 p $A      PDL

Matrix Operations

Matrix multiplication

 A * B     MATLAB
 $A x $B   PDL

Component-wise multiplication

 A .* B    MATLAB
 $A * $B   PDL

Transpose

 A'              MATLAB
 transpose $A    PDL

Mathematical Functions

Create a matrix of zeros

 A = zeros(5)      MATLAB
 $A = zeros 5,5    PDL

Create a matrix of ones

 A = ones(5)       MATLAB
 $A = ones 5,5     PDL

Create a random matrix

 A = rand(5)       MATLAB
 $A = random 5,5   PDL

Average of a matrix along one dimension

 mean(A)           MATLAB
 average $A        PDL

Average of all elements in a matrix

  mean(A(:))       MATLAB
  avg $A           PDL

Sum of a matrix along one dimension

  sum(A)           MATLAB
  sumover $A       PDL

Sum of all elements in a matrix

  sum(A(:))        MATLAB
  sum $A           PDL

Maximum of a matrix along one dimension

  max(A)           MATLAB
  maximum $A       PDL

Maximum of all elements in a matrix

  max(A(:))        MATLAB
  max $A           PDL

Minimum of a matrix along one dimension

  min(A)           MATLAB
  minimum $A       PDL

Minimum of all elements in a matrix

  min(A(:))        MATLAB
  min $A           PDL

Generate linearly spaced vector

  linspace(a,b,n)           MATLAB
  zeroes(n)->xlinvals(a,b)  PDL

Trig functions: sin, cos, tan, asin, acos, atan

Same in both languages.

Exponential and Log: exp, log, log10

Same in both languages.

Matrix dimensions

Dimension sizes

 size(A)      MATLAB
 shape $A     PDL      (see also dims $A which returns a perl list/array)

Number of dimensions

 ndims(A)     MATLAB
 ndims $A     PDL

Number of elements

 numel(A)     MATLAB
 nelem $A     PDL

Conditionals

A standard conditional ("if-statement") in Perl behaves like the one in MATLAB, with a more C-like syntax:

 % MATLAB conditional
  if value > MAX
     disp("Value too large")
  elseif value < MIN
     disp("Value too small")
  else
     disp("Value is perfect\n")
  end
 
 # Perl conditional
 if ($value > $MAX) {
     print "Value too large\n";
 } elsif ($value < $MIN) {
     print "Value too small\n";
 } else {
     print "Value is perfect\n";
 }

But unlike MATLAB, Perl has other conditionals that can make the code read more natural. For example, the "unless" statement behaves as the complement to "if":

 if ( ! error() ) {
     ... keep working ...
 }

 unless ( error() ) {
     ... keep working ...
 }

The second block reads more natural ("Unless there is an error, keep working"). Another way to make code more readable is to use Perl's post-fix notation for "if" and "unless":

  print "Warning: Value too large" if ( $value > $MAX );

  keep_working() unless ( invalid($value) );

Again, this can read very natural ("Keep working unless there is a problem"). Postfix notation is often used to highlight an error condition (as in the first example) or to express (in the code) that you expect a particular statement to get executed most of the time (as in the second example).

There is another conditional which will be familiar to C programmers:

 $result = ( valid($value) ? "ok" : "error" );

This is equivalent to the more verbose:

 if ( valid($value) ) {
     $result = "ok";
 } else {
     $result = "error";
 }

List of Matlab functions grouped

Names of the functions can be looked up in the list of Matlab's functions. You might also consider checking out Matlab's online documentation.

Desktop Tools and Development Environment

Feature	Matlab	Perl/PDL
Startup and Shutdown
Command to terminate interactive session	exit	exit, quit, x, q
Script file to run when closing	finish	Not available (?)
Startup config file	matlabrc	.perldlrc
Command Window and History

Data Import and Export

Feature	Matlab	Perl/PDL
Low-Level File I/O
Close a file	fclose	close
File attributes and path handling
Break a filename into path-and-name components	fileparts	File::Basename
Check that a file exists	??? error-free open?	-e operator
Search a directory tree	???	File::Find

Mathematics

Feature	Matlab	Perl/PDL
create a matrix of zeros	zeros	zeros, zeroes
create a matrix of [0,1] random numbers	rand	random
transpose	transpose, '	transpose
find average	mean	avg, average - for first dimension
find maximum	max	max, maximum - for first dimension
find minimum	min	min, minimum - for first dimension
inner product	a * b'	inner
outer product	a' * b	outer
sum of elements	sum - along columns	sumover - along 1st dimension (rows)
generate linearly spaced vector	linspace(a,b,n)	zeroes(n)->xlinvals(a,b);
Finding dimensions
dimension sizes	size	shape or dims
number of dimensions	ndims	ndims
number of elements	numel	nelem

Data Analysis

Programming and Data Types

Object-Oriented Programming

Graphics

3-D Visualization

GUI Development

External Interfaces

in ABC order

• abs - Core perl abs works on PDLs as well
• cat - see pdl(), cat(), and append() for PDL routines
• double - in PDL::Core
• end - in Perl complex expressions are wrapped by curly braces { }, no end keyword is used
• exit - Core perl exit, the finish.m probably maps to the END blocks in Perl
• function - Core perl sub,
• if - See the if statement in perldoc
• length - no easy "get the size of the longest dimension" here, calculate as pdl($pdl->dims)->max, see dims in PDL::Core
• magic - see http://search.cpan.org/dist/Math-MagicSquare-Generator or http://search.cpan.org/dist/Math-MagicSquare
• max - see List::Util for lists
• repmat - see PDL dummy() and clump() methods
• size(A) - see PDL shape() method, also dims() which returns perl list and not PDL vector of values
• size(A, N) - see PDL dim() method
• um2str
• unique - see PDL uniq() method for values and uniqvec() for unique(A,'rows')
• uniq_pairs
• unix - Core perl qx{} or backtick
• zeros - see PDL zeros()

Other terms

• M-files - Modules in Perl with .pm extentsion and the package keyword at the beginning and/or *.pdl files (see PDL::AutoLoader)
• Creating a matrix: $matrix = pdl( [[16, 3, 2, 13], [5, 10, 11, 8], [9, 6, 7, 12], [4, 15, 14 ,1] ] );
• sum($matrix) will return 136
• A' - transpose($matrix) from PDL::Basic

Toolbox

In this section we will list all the toolboxes that can be added to Matlab and see how they map to solutions using Perl and PDL.

Database Connectivity and Reporting

Perl (and thus PDL) can use DBI and the database drivers in the DBD::* namespace on CPAN