1PHILOSOPHY(1) User Contributed Perl Documentation PHILOSOPHY(1)
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6 PDL::Philosophy -- Why did we write PDL?
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9 Some history from the creator of PDL, leading into the philosophy and
10 motivation behind this data language. This is an attempt to summarize
11 some of the common spirit between pdl developers in order to answer the
12 question "Why PDL"?
13 The Start of PDL
15 "Why is it that we entertain the belief that for every purpose odd
16 numbers are the most effectual?" - Pliny the Elder
17 The PDL project began in February 1996, when I decided to experiment
19 with writing my own `Data Language'. I am an astronomer. My day job
20 involves a lot of analysis of digital data accumulated on many nights
21 observing on telescopes around the world. Such data might for example
22 be images containing millions of pixels and thousands of images of
23 distant stars and galaxies. Or more abstrusely, many hundreds of
24 digital spectra revealing the secrets of the composition and properties
25 of these distant objects.
26 Obviously many astronomers have dealt with these problems before, and a
28 large amount of software has been constructed to facilitate their
29 analysis. However, like many of my colleagues, I was constantly
30 frustrated by the lack of generality and flexibility of these programs
31 and the difficulty of doing anything out of the ordinary quickly and
32 easily. What I wanted had a name: "Data Language", i.e. a language
33 which allowed the manipulation of large amounts of data with simple
34 arithmetic expressions. In fact some commercial software worked like
35 this, and I was impressed with the capabilities but not with the price
36 tag. And I thought I could do better.
37 As a fairly computer literate astronomer (read "nerd" or "geek"
39 according to your local argot) I was very familiar with "Perl", a
40 computer language which now seems to fill the shelves of many
41 bookstores around the world. I was impressed by its power and
42 flexibility, and especially its ease of use. I had even explored the
43 depths of its internals and written an interface to allow graphics, the
44 ease with which I could then create charts and graphs, for my papers,
45 was refreshing.
46 Version 5 of Perl had just been released, and I was fascinated by the
48 new features available. Especially the support of arbitrary data
49 structures (or "objects" in modern parlance) and the ability to
50 "overload" operators - i.e. make mathematical symbols like "+-*/" do
51 whatever you felt like. It seemed to me it ought to be possible to
52 write an extension to Perl where I could play with my data in a general
53 way: for example using the maths operators manipulate whole images at
54 once.
55 Well one slow night at an observatory I just thought I would try a
57 little experiment. In a bored moment I fired up a text editor and
58 started to create a file called `PDL.xs' - a Perl extension module to
59 manipulate data vectors. A few hours later I actually had something
60 half decent working, where I could add two images in the Perl language,
61 fast! This was something I could not let rest, and it probably cost me
62 one or two scientific papers worth of productivity. A few weeks later
63 the Perl Data Language version 1.0 was born. It was a pretty bare
64 infant: very little was there apart from the basic arithmetic
65 operators. But encouraged I made it available on the Internet to see
66 what people thought.
67 Well people were fairly critical - among the most vocal were Tuomas
69 Lukka and Christian Soeller. Unfortunately for them they were both Perl
70 enthusiasts too and soon found themselves improving my code to
71 implement all the features they thought PDL ought to have and I had
72 heinously neglected. PDL is a prime example of that modern phenomenon
73 of authoring large free software packages via the Internet. Large
74 numbers of people, most of whom have never met, have made contributions
75 ranging for core functionality to large modules to the smallest of bug
76 patches. PDL version 2.0 is now here (though it should perhaps have
77 been called version 10 to reflect the amount of growth in size and
78 functionality) and the phenomenon continues. I firmly believe that PDL
79 is a great tool for tackling general problems of data analysis. It is
80 powerful, fast, easy to add too and freely available to anyone. I wish
81 I had had it when I was a graduate student! I hope you too will find
82 it of immense value, I hope it will save you from heaps of time and
83 frustration in solving complex problems. Of course it can't do
84 everything, but it provides the framework, the hammers and the nails
85 for building solutions without having to reinvent wheels or levers.
86 --- Karl Glazebook, the creator of PDL
88 Major ideas
90 The first tenet of our philosophy is the "free software" idea: software
91 being free has several advantages (less bugs because more people see
92 the code, you can have the source and port it to your own working
93 environment with you, ... and of course, that you don't need to pay
94 anything).
95 The second idea is a pet peeve of many: many languages like Matlab are
97 pretty well suited for their specific tasks but for a different
98 application, you need to change to an entirely different tool and
99 regear yourself mentally. Not to speak about doing an application that
100 does two things at once... Because we use Perl, we have the power and
101 ease of Perl syntax, regular expressions, hash tables, etc. at our
102 fingertips at all times. By extending an existing language, we start
103 from a much healthier base than languages like Matlab which have grown
104 into existence from a very small functionality at first and expanded
105 little by little, making things look badly planned. We stand by the
106 Perl sayings: "simple things should be simple but complicated things
107 should be possible" and "There is more than one way to do it"
108 (TIMTOWTDI).
109 The third idea is interoperability: we want to be able to use PDL to
111 drive as many tools as possible, we can connect to OpenGL or Mesa for
112 graphics or whatever. There isn't anything out there that's really
113 satisfactory as a tool and can do everything we want easily. And be
114 portable.
115 The fourth idea is related to "PDL::PP" and is Tuomas's personal
117 favorite: code should only specify as little as possible redundant
118 info. If you find yourself writing very similar-looking code much of
119 the time, all that code could probably be generated by a simple Perl
120 script. The PDL C preprocessor takes this to an extreme.
121 Minor goals and purposes
123 We want speed. Optimally, it should ultimately (e.g. with the Perl
124 compiler) be possible to compile "PDL::PP" subs to C and obtain the top
125 vectorized speeds on supercomputers. Also, we want to be able to
126 calculate things at near top speed from inside Perl, by using dataflow
127 to avoid memory allocation and deallocation (the overhead should
128 ultimately be only a little over one indirect function call plus couple
129 of ifs per function in the pipe).
130 Go on, try it!
132 Well, that's the philosophy behind PDL - speed, conciseness, free,
133 expandable, and integrated with the wide base of modules and libraries
134 that Perl provides. Feel free to download it, install it, run through
135 some of the tutorials and introductions and have a play with it.
136 Enjoy!
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140 Added Karl Glazebrook (2001) contributions by Matthew Kenworthy
141 Copyright(C) 1997 Tuomas J. Lukka (lukka@fas.harvard.edu).
143 Redistribution in the same form is allowed but reprinting requires a
145 permission from the author.
146perl v5.32.0 2020-09-17 PHILOSOPHY(1)