Matteo's Wasps' Nest » English

Generating all combinations of n elements taken t at a time

Matteo — Thu, 08 Mar 2012 18:38:09 +0000

I don’t usually share the code I write for my research projects, unless someone asks for it. Anyway, today I had fun writing some C code, and I think it may turn out to be useful for other people. It’s written almost well enough to be acceptable, so here you are.

I implemented Chase’s sequence algorithm to generate the bit-strings corresponding to each combination of n elements taken t at a time. The algorithm is described in Donald E. Knuth’s “The Art Of Computer Programming”, Vol. 4, Fasc. 3, page 13. I implemented it in C and added very few comments, so refer to TAOCP if you have any doubts.

The code is distributed under the BSD 2-clauses License.

Download chaseseqcombgen.c

Posted from Providence, Rhode Island, United States.

On Rejections

Matteo — Wed, 15 Feb 2012 02:28:50 +0000

One has to learn to accept rejections. They trim down your ego, help you put things back in prospective, give you the right amount of hanger to fight back.

Not everyone appreciate what we do as we think we appreciate it. Feedback is what make mankind progress, especially the negative but constructive type.

Posted from Providence, Rhode Island, United States.

Drops of wisdom, food for thoughts.

Matteo — Thu, 15 Dec 2011 08:16:27 +0000

I am still reading Vapnik’s The Nature of Statistical Learning Theory. I began reading it a first time in March, but then left it aside for months, so I started over in October. It’s enlightening and a pleasure to read, if one can stay focused.

Every now and then, Vapnik lets drops of wit fall on the pages, and the reader that can spot them is able to savour the wisdom of a great mind.

I like this one, which was “buried” in a footnote on page 13:

“Of course it is very interesting to know how humans can learn. However, this is not necessarily the best way for creating an artificial learning machine. It has been noted that the study of birds flying was not very useful in constructing the airplane.”

Interesting thought, and nice counterexample. =)

Posted from Providence, Rhode Island, United States.

Why doing research?

Matteo — Wed, 19 Oct 2011 14:10:32 +0000

There is so much I still do not know that I wonder what right I have to try to increase knowledge with my research instead of burying myself in a library and just read what the giants did. I am not limiting this to any specific field: I would like to read about literature, science, visual art, music, philosophy, …

Posted from Providence, Rhode Island, United States.

Darkroom night

Matteo — Wed, 05 Oct 2011 01:35:46 +0000

Tonight I went to the darkroom just to develop one roll of t-max 100 film from the Mamiya 7. Relax, fun, quiet: everything I could ask for. I’m happy that I went even if it was raining and I wasn’t feeling safe on my bike.

Photo geek note: I’m in love with my Kodak Process Type 3 Thermometer.

The next two months will be “printing months”, because I want to come to Italy for Christmas with a bag full of prints, from 6×7 and 35mm, to give to friends and family as presents.

Posted from Providence, Rhode Island, United States.

Speedy update

Matteo — Sun, 25 Sep 2011 12:58:43 +0000

This is the kind of post I don’t like to write, but I’m writing one now anyway. It’s just to say that I have very little time to blog about “serious” stuff, meaning “to write very/too long posts in Italian with some philosophical references“. My research is taking “away” a lot of time, I started going to the AS220 darkroom to develop and print my pictures twice a week, a new tango class just started. But everything is going well. Very well.

There’s a light in the dark(room)

Matteo — Wed, 24 Aug 2011 03:49:37 +0000

I’m just back from a printing session in the AS220 Paul Krot Darkroom. I’m just back from four hours of fun.

I stink now. I stink of chemicals. I stink of light.

My last time in the darkroom was I don’t even know how far in the past, around 18 months probably. My technique is rusty. It has never been shiny anyway, but I did a lot of mistakes this time: no worries, there’s room for improvement. A lot of room for improvement.

But I’m happy of my approach. It’s the beginning of something new, of a more confident approach, of a more I-(think)-I-know-what-I-want approach. Of a more educated approach too: in the past week or so I read David Vestal’s The Craft of Photography again, just to refresh my memory about what materials I needed for printing, and what steps are involved in the process. Now it’s the turn of Ansel Adams’ The Print, which I got as a present for my birthday in 2010, but never really read with the necessary attention. Both books are pretty out-of-date as far as the discussed materials are concerned, but what I’m trying to get this time is the approach, the mentality, the philosophy if you wish (I don’t) of printing.

I started keeping a darkroom notebook, to keep a record of what I’m doing and how. This already proved to be very useful since this first printing session, and I know that some details were missing. It’s a work in progress. It’s a process. Like printing. Like learning. Like learning to print.

I’m going back next Tuesday. I’m actually going back tomorrow, to get my dried prints. Will I be able to sleep or will I dream of dark and light making love in a pool of developer?

Posted from Providence, Rhode Island, United States.

What being nerd means, from time to time…

Matteo — Mon, 22 Aug 2011 03:09:43 +0000

I was planning on posting something new about my relationship with photography, but then I got lost tweaking my WordPress installation, upgrading plugins, making sure themes don’t give errors, etc. etc….which means I spent more or less two hours on my wordpress admin panel, on FTP uploads, on editing files in VIM, etc. etc. . It also means I’m not publishing anything new about photography, but given that I could not accept a complete defeat by my nerdiness, I at least manage to publish this post. Better than noting, or not?

Posted from Providence, Rhode Island, United States.

Are complex theories practical?

Matteo — Tue, 26 Apr 2011 16:29:38 +0000

The end of my second year as a Ph.D. student is getting close and I must start thinking about a dissertation topic. At least, I already have some ideas about the areas of my dissertation: databases, data mining, and modern statistics and learning theory. The problem of learning drew my interest since I discovered there was a problem of learning, i.e., in philosophy class in high school. Being the grandchild of a philosopher, I just could not resist and I started wondering about knowledge and how we acquire it. Still, I have to admit I did not read much of the opinions of great thinkers of the past and the present on the matter.

Anyway, the following is a passage from the Preface to the First Edition of Vladimir N. Vapnik’s The Nature of Statistical Learning Theory, 2^nd Ed.

[…] during the last few years at different computer science conferences, I heard reiteration of the following claim:

Complex theories do not work; simple algorithms do.

[…] I would like to demonstrate that in this area of science^[1] a good old principle is valid:

Nothing is more practical than a good theory.

Vapnik does not say (at least in this Preface) whether a “good” theory could also be simple or actually have to be complex, nor whether the complexity of the theory has any significance on its being “good”.

Still, I like this passage. It is bold, effective, and probably true, especially in the part regarding computer scientists’ point of view.

1. ^ statistical inference.

Posted from Providence, Rhode Island, United States.

Machine Learning and Theory

Matteo — Mon, 14 Mar 2011 23:00:38 +0000

This is exactly the point and is where I want to take my research!

“Machine Learning has become a very mathematical and statistical-based research area yet the theoretical computer science community hasn’t played the role in this area that we could have.”

From a blog post by Lance Fortnow

Posted from Providence, Rhode Island, United States.