December 21, 2005

Reading Time: 2 minutes

Last Updated on December 25, 2005 by stlplace

My car is making funny noise recently. So I made an appointment with a local Nissan dealership 9AM today, to take a look. The customer rep asked my phone numbers and the usual stuff. I gave them both my work number and mobile number (that turns out to be a mistake). He told me expect an hour and half before getting back to me. The dealership is about 20 minutes walk from my home. On the way back to home, I decided to work remotely using VPN so that I don’t need to ask somebody giving me a ride or rent a car. I started work using Remote Desktop and fixed the problem I mentioned in the previous post. There are a few glitches such as “Network disconnected” or slow response from Graphic intensive applications. But in general I am pleased with the performance of Microsoft Remote Desktop.

When I was happily working on computer, I forgot one thing — call the dealership more often. I did give them a call at 12:30 PM and they told me they still have not figured out the cause of noise. So I figured give them some breeze time. I had some sympathy for them because I am doing similar things such as they do: debugging computer problem vs. car problem. But they did not call my cell phone. When I walked to the dealership at 6PM, they told me they called my work number and left a message. Dahn! They did find the cause of the problem, but they did not fix it without my permission. Now I have to wait till tomorrow morning to pick up my car. I can take another 20 minutes walk. But I was disappointed by them not calling my cell phone number earlier.

This reminds me of something I experienced in Toyota dealership when I was shopping my first new car years ago. I was going to buy a Toyota at two dealerships but both of them have a “either buy it at my price; or just leave” attitude. So I ended up not buying it.

Japanese car companies, Toyota, Honda and Nissan are having a good time these days in the US market. Their quality and reliability are undisputed. But their customer service…I don’t want to talk about it.

Chasing the bug round 2

Reading Time: < 1 minute

Last Updated on May 28, 2009 by stlplace

I was pretty stressed out debugging a problem last two weeks. Luckily I saw the light at the end of the tunnel yesterday. I found out the cause: the tolerance of transform matrix. This is a tough problem because it appears to me the problem occurred without any pattern. But later on I realized out of all the randomness, there is something in common: the misplaced components all end up in the same place. I implemented the fix this morning and it worked like a champ.

Tolerance played an important role in my world. I guess it’s just a way of life. The problem is the computer can not represent a number accurately. Say an inch is 25.4 mm, but in computer it is really 25.399999…If you convert the inch to mm and then convert it back, it maybe something like 25.398888. Now if you do a comparason of this number with 25.4, it won’t be equal any more. Similar things can happen for vectors, matrix, geometries, etc.

There are called rounded errors in numerical computation. I took a course on numerical computation in graduate school in Rolla. The theory was a bit abstract. But now I got the fun to play with the real stuff. It’s not as complicated as one might think.