Trung Huynh's tech blog http://www.trungh.com Even god made mistakes, please let me know what mistakes I have made Tue, 11 Oct 2011 14:20:51 +0000 en hourly 1 http://wordpress.org/?v=3.0.3 The “Michael Dell” Meeting http://www.trungh.com/2011/10/the-%e2%80%9cmichael-dell%e2%80%9d-meeting/ http://www.trungh.com/2011/10/the-%e2%80%9cmichael-dell%e2%80%9d-meeting/#comments Tue, 11 Oct 2011 11:55:20 +0000 trung http://www.trungh.com/2011/10/the-%e2%80%9cmichael-dell%e2%80%9d-meeting/ The below talk was given shortly after Steve Jobs returned in 1997 as Interim CEO, in response to Michael Dell’s suggestion in the press a few days previous that Apple should just shut down and return the cash to shareholders:

And you know what? He’s right.

The world doesn’t need another Dell or HP. It doesn’t need another manufacturer of plain, beige, boring PCs. If that’s all we’re going to do, then we should really pack up now.

But we’re lucky, because Apple has a purpose. Unlike anyone in the industry, people want us to make products that they love. In fact, more than love. Our job is to make products that people lust for. That’s what Apple is meant to be.

What’s BMW’s market share of the auto market? Does anyone know? Well, it’s less than 2%, but no one cares. Why? Because either you drive a BMW or you stare at the new one driving by. If we do our job, we’ll make products that people lust after, and no one will care about our market share.

Apple is a start-up. Granted, it’s a startup with $6B in revenue, but that can and will go in an instant. If you are here for a cushy 9-to-5 job, then that’s OK, but you should go. We’re going to make sure everyone has stock options, and that they are oriented towards the long term. If you need a big salary and bonus, then that’s OK, but you should go. This isn’t going to be that place. There are plenty of companies like that in the Valley. This is going to be hard work, possibly the hardest you’ve ever done. But if we do it right, it’s going to be worth it.

– Steve Jobs

The story is reblogged from Adam Nash’s blog

]]> http://www.trungh.com/2011/10/the-%e2%80%9cmichael-dell%e2%80%9d-meeting/feed/ 0 People think focus means saying yes to t… http://www.trungh.com/2011/10/focus-ability-to-say-no/ http://www.trungh.com/2011/10/focus-ability-to-say-no/#comments Wed, 05 Oct 2011 10:11:33 +0000 trung http://www.trungh.com/2011/10/focus-ability-to-say-no/ People think focus means saying yes to the thing you’ve got to focus on. But that’s not what it means at all. It means saying no to the hundred other good ideas that there are. You have to pick carefully.

Steve Jobs

]]> http://www.trungh.com/2011/10/focus-ability-to-say-no/feed/ 0 Remembering that you are going to die is… http://www.trungh.com/2011/09/remembering-that-you-are-going-to-die-is-2/ http://www.trungh.com/2011/09/remembering-that-you-are-going-to-die-is-2/#comments Wed, 07 Sep 2011 20:25:23 +0000 trung http://www.trungh.com/2011/09/remembering-that-you-are-going-to-die-is-2/ Remembering that you are going to die is the best way I know to avoid the trap of thinking you have something to lose. You are already naked. There is no reason not to follow your heart.

Steve Jobs

]]> http://www.trungh.com/2011/09/remembering-that-you-are-going-to-die-is-2/feed/ 0 Success is the ability to go from one fa… http://www.trungh.com/2011/08/success-is-the-ability-to-go-from-one-fa/ http://www.trungh.com/2011/08/success-is-the-ability-to-go-from-one-fa/#comments Thu, 18 Aug 2011 10:03:56 +0000 trung http://www.trungh.com/2011/08/success-is-the-ability-to-go-from-one-fa/ Success is the ability to go from one failure to another with no loss of enthusiasm.

Winston Churchill

]]> http://www.trungh.com/2011/08/success-is-the-ability-to-go-from-one-fa/feed/ 0 THE FUTURE IS ALREADY HERE, IT’S JUST UN… http://www.trungh.com/2011/07/the-future-is-already-here-it%e2%80%99s-just-un/ http://www.trungh.com/2011/07/the-future-is-already-here-it%e2%80%99s-just-un/#comments Tue, 19 Jul 2011 10:46:39 +0000 trung http://www.trungh.com/2011/07/the-future-is-already-here-it%e2%80%99s-just-un/ THE FUTURE IS ALREADY HERE, IT’S JUST UNEVENLY DISTRIBUTED

WILLIAM GIBSON, 1994

]]> http://www.trungh.com/2011/07/the-future-is-already-here-it%e2%80%99s-just-un/feed/ 0 Google vs Microsoft (search, google docs… http://www.trungh.com/2011/07/google-vs-microsoft-search-google-docs/ http://www.trungh.com/2011/07/google-vs-microsoft-search-google-docs/#comments Mon, 18 Jul 2011 10:00:08 +0000 trung http://www.trungh.com/2011/07/google-vs-microsoft-search-google-docs/ Google vs Microsoft (search, google docs, android, gmail) + Facebook (G+) + Twitter (Buzz) + Apple (Android) + Groupon (Google Deals) + Foursquare (Google Latitude) + Yahoo (Search, Google News, Google Talk) + BBC (Google News) + Vimeo (YouTube) +…, c’mon greedy Google, this is not your own world!

]]> http://www.trungh.com/2011/07/google-vs-microsoft-search-google-docs/feed/ 0 An Introduction to Sentiment Analysis http://www.trungh.com/2011/06/an-introduction-to-sentiment-analysis/ http://www.trungh.com/2011/06/an-introduction-to-sentiment-analysis/#comments Thu, 30 Jun 2011 09:42:24 +0000 trung http://www.trungh.com/2011/06/an-introduction-to-sentiment-analysis/

]]> http://www.trungh.com/2011/06/an-introduction-to-sentiment-analysis/feed/ 0 reassign user/group for sshfs mounted device http://www.trungh.com/2011/04/reassign-usergroup-for-sshfs-mounted-device/ http://www.trungh.com/2011/04/reassign-usergroup-for-sshfs-mounted-device/#comments Wed, 13 Apr 2011 10:16:45 +0000 trung http://www.trungh.com/2011/04/reassign-usergroup-for-sshfs-mounted-device/
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sshfs -o allow_other,uid={new uid},gid={new gid} {remote address} {mounted address}
]]> http://www.trungh.com/2011/04/reassign-usergroup-for-sshfs-mounted-device/feed/ 0 git/git-svn notes http://www.trungh.com/2011/03/gitgit-svn-notes-2/ http://www.trungh.com/2011/03/gitgit-svn-notes-2/#comments Wed, 23 Mar 2011 16:19:04 +0000 trung http://www.trungh.com/2011/03/gitgit-svn-notes-2/ Untrack a file (works nice with git-svn):

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git update-index --assume-unchanged file_to_untrack
]]> http://www.trungh.com/2011/03/gitgit-svn-notes-2/feed/ 0 An introduction to Q-learning http://www.trungh.com/2011/03/an-introduction-to-q-learing/ http://www.trungh.com/2011/03/an-introduction-to-q-learing/#comments Tue, 22 Mar 2011 18:05:35 +0000 trung http://www.trungh.com/2011/03/an-introduction-to-q-learing/ Q-learning [Watkins, 1989] is one of the most popular reinforcement learning methods. One of the advantages of Q-learning is its ability to compare the expected utility of the available actions without requiring a model of the environment.

The basic content of Q-learning is inside the below equation:

Q_{t+1}(a, s)=(1-\alpha_{t})Q_{t}(a,s)+\alpha_{t}[r_{t}(s)+\gamma\max_{a^{'}}{Q_{t}(a',s')}]

Where:

  • Q_{t}(a,s) is the Q-value at time t, state s with action a.
  • r_{t} is the reward.
  • \alpha is the learning rate. The learning rate determines how fast and how important the new information is to be learned. If \alpha is 0, the agent does not learn anything. If \alpha is 1, only the new information is considered and all old information is discarded.
  • \gamma is the discount factor. The discount factor is in range [0..1] and is used to weight new term reinforcement more heavily than distant future reinforcement. The closer \gamma is to 1, the greater the weight of future reinforcement.

So what does the equation mean ? We now assume \alpha=1 and \gamma=1, then the equation becomes:

Q_{t+1}(a, s)=r_{t}(s)+max_{a'}{Q_{t}(a',s')}

It is now easy to see that the Q-value of state-action pair (a,s) is equal to the maximum Q-value of next state (for all next actions) adding the reward of action a. The learning method is obviously a dynamic algorithm that gives the optimal Q-value for state-action pairs.

When the discount factor is enabled (<1),  it makes the reward reduced by time and hence the total reward at time t is given by:

R_{t}=r_{t}+\gamma r_{t+1} + \gamma^2 r_{t+2} + \dots + \gamma^n r_{t+n} + \dots

The bellow java applet is a very good illustration of Q-learning (thank to Vander B. Frank):

For the detail of how the applet works, please reach the document of Vander B. Frank through this PDF.



Bibliography

1. Wikipedia: Q-learning [http://en.wikipedia.org/wiki/Q-learning].
2. Vander B. Frank: Q-learning. IRIDIA, Universit Libre de Bruxelles. 7, 2003. [PDF]
3. Watkins, C.J.C.H. (1989). Learning from Delayed Rewards. PhD thesis, Cambridge University, Cambridge, England

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