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Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

© 2006-2015 Andrew Cooke (site) / post authors (content).

[Computing] Change to ssh handling of multiple identities?

From: andrew cooke <andrew@...>

Date: Thu, 22 Feb 2018 16:53:19 -0300

Just in case anyone else has hit this (only applicable if you have
multiple github accts and use the HostName hack to select keys).

I have multiple github accounts (personal use and work), and each has
a separate ssh key.  This is described at

And that has always worked fine, until today.

Today I saw:

  > ssh -T git@...-isti
  Hi andrewcooke! You've successfully authenticated, but GitHub does not provide shell access.

which is WRONG.  with and the "trick" above, I should
be identified as andrewcooke-isti (and so cannot clone or pull or push
to any work code...)

The fix is to add "IdentitiesOnly yes" to the ssh config:

  > cat ~/.ssh/config

       User git
       IdentityFile ~/.ssh/id_rsa-isti
       IdentitiesOnly yes

I have no idea what changed (could this be OpenSuse config specific?),
but hopefully this will save someone else the pain of debugging...


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[Bike] Endura Hummvee Lite II

From: andrew cooke <andrew@...>

Date: Mon, 12 Feb 2018 10:58:06 -0300

Just received a pair of these shorts in the mail.

The old model were my main cycle shorts for years (I think I have four
pairs kicking around somewhere).  They're tough, comfortable, and
relatively cool in the heat.  More recently I've switched mainly to
bibs, but I still wanted a pair of shorts for the occasional ride and
also for the gym, and the old ones were really starting to show their
age (as well as suffering a few rips from falls over the years).

The main idea of the Lite was that they're for hot weather, so use
thinner material, although the seat of the pants remains something
thicker so they don't wear out.  That hasn't changed, but the look of
the material has improved - the grey colour I bought has a visible
texture like a natural fibre (my old light grey ones were obviously
nylon).  They also have a blue highlight (the pocket zip - more on
pockets below) that I guess looks more modern (not sure I'm a fan
myself, but it's a small detail).

Another change is the use of a button at the waist rather than snap
fasteners - probably an improvement, although (for me, at least) the
fasteners stayed closed fine on the older model.  The clickfast liner,
also using snap fasteners, remains as before.

But the two biggest changes are pockets and legs.

The cut of the legs is noticeably thinner, but they no longer have the
velcro width adjuster.  That's probably a good thing - they were so
wide they tended to get caught on my pump (mounted on the down tube)
at times, while tightening them with the adjusters looked really
(really) dumb.  But could this mean they are less cool when riding?

The old style had two leg pockets (one larger than the other).  The
new style has one leg pocket and one rear pocket.  A rear pocket is a
good idea - the leg pockets flapped annoyingly if you carried
something heavy like keys.  BUT the leg remaining leg pocket is
smaller than the old large pocket.  That means that you can no longer
fit a quarter-folded sheet of (letter) paper in there (maybe I am the
only person who takes print-outs of maps and routes on rides?).
Hummvee are generally well-known for their pockets, so this seems like
a step backwards.  Keeping both leg pockets and adding an extra at the
rear would have been better.

I've not ridden with these yet, but overall I think they're probably a
slight improvement.  The new fabric certainly looks nicer, and the
narrower fit is probably more practical, even if I wish there was
still a large leg pocket.



Sanity Check For Nuclear Launch

From: andrew cooke <andrew@...>

Date: Sat, 10 Feb 2018 17:44:38 -0300

  My suggestion was quite simple: Put that needed code number in a
  little capsule, and then implant that capsule right next to the
  heart of a volunteer. The volunteer would carry with him a big,
  heavy butcher knife as he accompanied the President. If ever the
  President wanted to fire nuclear weapons, the only way he could do
  so would be for him first, with his own hands, to kill one human
  being. The President says, “George, I’m sorry but tens of millions
  must die.” He has to look at someone and realize what death is—what
  an innocent death is. Blood on the White House carpet. It’s reality
  brought home.

  When I suggested this to friends in the Pentagon they said, “My God,
  that’s terrible. Having to kill someone would distort the
  President’s judgment. He might never push the button.“



Entropy and Life

From: andrew cooke <andrew@...>

Date: Sun, 4 Feb 2018 19:23:15 -0300



[Link, Bike] Cheap Cycling Jerseys

From: andrew cooke <andrew@...>

Date: Thu, 4 Jan 2018 20:13:58 -0300

I just received this jersey from Amazon and it seems pretty good (nice
fit, vibrant colours - no idea how durable yet)

But then I realised that teh same jerseys are available cheaper on

Here are my favourites so far (I should get a Pinterest):
(but select the dark one with a pink stripe).
(and, same link, select the grey/green/blue one; also maybe the light
blue one).



[Link, Music] Music To Steal 2017

From: andrew cooke <andrew@...>

Date: Sun, 17 Dec 2017 12:18:23 -0300



[Link, Future] Simulated Brain Drives Robot

From: andrew cooke <andrew@...>

Date: Tue, 12 Dec 2017 08:42:24 -0300

A simulated worm's brain drives a robot.

I have been re-reading William Gibson's work.  This just seemed so on
the money.



[Link, Computing] Learned Index Structures

From: andrew cooke <andrew@...>

Date: Tue, 12 Dec 2017 08:41:20 -0300

(frankly I think this paper i smore important than credited in that
discussion - we'll see...).



[Bike] Exercise And Fuel

From: andrew cooke <andrew@...>

Date: Sat, 9 Dec 2017 15:40:35 -0300

"Fuel" rather than "Nutrition" because I am thinking mainly about the
calories.  The following thoughts were prompted by a paper I read
online which I can no longer find - repeating the search leads me to
other, more complex studies.  So not only do I not have a reference,
but what follows may be oversimplified.

Glycogen v Fat

When exercising aerobically we burn fuel from three main sources:

 * Fat reserves, which are virtually unlimited (for most of us), but
   slow to access.  Fat reserves are stored throughout the body.

 * Glycogen reserves, which are limited but easier to access.
   Glycogen reserves are local to the muscle being used.

 * External sources (ie eating).

At low exertion levels the body preferentially burns fat.  But as the
power output increases this cannot be accessed quickly enough and the
proportion of glycogen increases.

Since the amount of glycogen is limited this explains "bonking" or
"the wall" - the unpleasant experience of glycogen reserves being
depleted.  As you would expect, this can be postponed by:

 * Lowering power output (and so reducing both absolute and relative
   burn rates for glycogen)

 * Increasing glycogen reserves.  Either via training or carb-loading.

 * Eating while exercising.  An external source of fuel will displace
   the need for glycogen / fat burning, but is limited in volume (you
   simply can't eat that much while exercising) and delayed (it takes
   time to digest what you eat).

Given all the above it is clear that the need to eat while doing
endurance exercise will depend on both the size of glycogen reserves
and the power levels required - both of which can vary strongly from
person to person.

Glycemic Complexity

One factor briefly mentioned above is digestion time.  High glycemic
index carbs are those that are easy to digest and provide a large
amount of energy for a short time, while low index carbs are slow to
digest, providing a lower, more extended boost.

Curiously, the index doesn't match the difference between simple and
complex sugars: white bread (starch) apparently has a higher index
than sugar (sucrose).

This is important for me because, it turns out, the time I stop riding
to eat is quite significant in how well I perform (over longer
segments on Strava).  So I guess I should look eating porridge before
a ride...



[Maths, Link] Dividing By Zero

From: andrew cooke <andrew@...>

Date: Sat, 4 Nov 2017 09:53:34 -0300



[Book, Review] Ray Monk - Ludwig Wittgenstein: The Duty Of Genius

From: andrew cooke <andrew@...>

Date: Fri, 3 Nov 2017 08:59:38 -0300

This is a curious mix of a book.

On the one hand, it's well written - clear and coherent.  A deftly
constructed account of Wittgenstein's life, painting an apparently
complete picture of its subject.

On the other - at least to this reader - it fails to explain exactly
why Wittgenstein was (and is) so admired.  Trudging through the
details of his obsessions, neuroses and fears, you begin to wonder why
you are spending so much time (~600 pages) on such an unpleasant

 * Someone who gave up a huge amount of wealth, but continued to
   assume the privilege and standing of his birth, repeatedly relying
   on the influence of friends in high places.

 * Someone pathetically useless in social situations who felt
   qualified to tell others how they should behave.  Who was incapable
   of being a good teacher yet encouraged others to follow the same

 * Someone who intimidated and brow-beat.  Whose philosophy appears to
   be "I am right, you are wrong, but I cannot explain why."

 * Someone who felt they were making major contributions to the
   philosophy of mathematics yet lacked the technical ability to
   understand Godel's work.

 * Someone who could only connect emotionally with those who were
   younger, weaker, and easier to intimidate.

A thoroughly unlikeable man.

I am not arguing that only the nicest people should have biographies,
but perhaps the author should more clearly explain why they are
interesting.  Reports of "genius" from others in the same privileged
milieu are not enough.