Comments for 4by12

Comment on A Short Note on the Poincaré Algebra by Dan Elharrar

Dan Elharrar — Mon, 25 May 2009 10:44:34 +0000

To me, and to generations of French kids, there is only one Casimir.

Comment on Correct arXiv authors in Google Reader by ggg

ggg — Tue, 19 May 2009 09:31:11 +0000

thanks for this, I have been waiting for ages for Google to fix this problem!

Comment on Complex Square Root by Guy Gur Ari

Guy Gur Ari — Tue, 24 Mar 2009 15:16:51 +0000

Yes of course. Perhaps the post was not clear. My only point is this: With the reals, the mistake is easy to spot. More importantly, one can work with a definition (sqrt = positive root), using which algebra behaves as you expect.

With the complex numbers the mistake is more subtle, and there is no such convenient definition for sqrt. Seemingly innocent manipulations often conceal mistakes, as one must always be careful when crossing the branch cut.

Comment on Complex Square Root by jascha

jascha — Tue, 24 Mar 2009 10:24:28 +0000

uh-oh. I think it might be spreading to the reals! Proof that 1 = -1:

sqrt(1) = 1
sqrt(1) = -1

1 = sqrt(1)/sqrt(1) = 1/-1 = -1

Comment on Legendre Transform by jascha

jascha — Tue, 24 Mar 2009 10:19:46 +0000

Thanks for writing this up! I found it really helpful.

Comment on It’s like deja vu all over again by Guy Rosen

Guy Rosen — Thu, 13 Nov 2008 09:24:56 +0000

Looks like it’s burst

Comment on Ubuntu Installation Update by TC

TC — Sun, 17 Feb 2008 16:13:52 +0000

Installed Ubuntu 7.10 Gutsy yesterday and found myself here again looking for that desktop!

This is my first step into the Linux arena, and I am quite impressed. Lots of learning ahead!

Thanks a million!

Comment on A Google plugin for deskbar-applet by Guy Gur Ari

Guy Gur Ari — Wed, 06 Feb 2008 21:19:47 +0000

Hm…. I’m not using this anymore, sorry. I expect it shouldn’t be difficult if you know a bit of programming.

Comment on A Google plugin for deskbar-applet by Kenny

Kenny — Thu, 31 Jan 2008 08:09:25 +0000

Any chance of getting this to work in 2.20?

Comment on Fun with PDEs by 4by12 » Archive » Fun With PDEs - Part 2

4by12 » Archive » Fun With PDEs - Part 2 — Mon, 17 Sep 2007 03:42:42 +0000

[...] Last time I described the first pitfall I encountered when solving a PDE — an inherent instability in the partial derivatives. This time I’ll talk about the second pitfall, which is simpler conceptually, but has wider implications for programming in general. [...]