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PDL::Intro - Introduction to the Perl Data Language

Version 2.4

"Why is it that we entertain the belief that for every purpose odd numbers are the most effectual?" - Pliny the Elder.

Karl Glazebrook [] and Craig DeForest [


Perl Data Language (PDL) is a perl extension that is designed for scientific and bulk numeric data processing and display. It extends perl's syntax and includes fully vectorized, multidimensional array handling, plus several paths for device-independent graphics output.

pdl is an interactive command shell that is supplied with PDL; for more information, see perldl(1).

Because PDL is a modular extension to perl, it is accessible to ordinary perl scripts: to write a command-line PDL script you just say "use PDL;" at the top of an ordinary perl script. There is also a specialized interactive shell (perldl(1)) that allows you to issue PDL commands interactively and that includes a path-based subroutine autoloader similar to those found in MatLab and IDL (which are trademarks of MathWorks and Kodak, respectively). The perldl shell allows you to quickly manipulate and "play with" your data. (You can also invoke it with the shorter command "pdl").

The PDL module is a complete Object-Oriented extension to Perl (although you don't have to know what an object is to use it) which allows large N-dimensional data sets, such as large images, spectra, time series, etc to be stored efficiently and manipulated en masse. For example with the PDL module we can write the perl code $a=$b+$c, where $b and $c are large datasets (e.g. 2048x2048 images), and get the result in only a fraction of a second.

PDL variables (or piddles as they have come to be known) support a wide range of fundamental data types - arrays can be bytes, short integers (signed or unsigned), long integers, floats or double precision floats. And because of the Object-Oriented nature of PDL new customised datatypes can be derived from them.

Perl is an extremely good and versatile scripting language, well suited to beginners, and allows rapid prototyping. The PDL extensions to the language use Perl's object-oriented capabilities to seamlessly add high-speed scientific capabilities that are themselves written in perl, C and/or FORTRAN as appropriate -- so your code's "hot spots" run at native compiled-language speed, while you work in the higher level perl language (which itself runs faster than many other JIT-compiled or interpreted languages).

External modules that have been incorporated into PDL include the complete Gnu Scientific Library; CFITSIO for FITS file handling; FFTW; the Slatec matrix-handling package; and the PGPLOT, PLPLOT, Karma, and OpenGL graphics libraries. Ancillary packages written in PDL itself include image handling, curve fitting, matrix manipulation, coordinate transformation, nonlinear data resampling, graphics I/O, and extensive file I/O utilities. Because PDL programs are "just" perl with additional modules loaded, the entire CPAN archive is also available to your PDL scripts.


This manual page provides a general introduction to the underlying philosophy of PDL. For an overview over the rest of the documentation see PDL::Index. As a beginner the following documents are particulary recommended:


Quick summary - PDL for the impatient


The Frequently Asked Questions list for PDL.


Why another matrix language?


An introduction to using smart indices in PDL.


The all important slicing of piddles.


Copyright (C) Karl Glazebrook (, Tuomas J. Lukka, ( and Christian Soeller ( 1997-2002.

Commercial reproduction of this documentation in a different format is forbidden without permission.

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