Thursday, July 2, 2015

Wordpress with MySQL: Error establishing a database connection

The Problem

I ran into the following problem today when I was setting up a fresh local wordpress install on my Mac.

"Error establishing a database connection
This either means that the username and password information in your wp-config.php file..."
Fortunately, the fix was pretty simple!

The Fix

First, check if MySQL is running:
In terminal, I typed
mysqladmin version

If the server is running, the above command should return something like:

So the server is running, and I'm 100% sure I have the right username and password. So, what's the problem?
On a whim, I found the fix:
In /<wordpress folder>/wp-config.php, change the line
define('DB_HOST', 'localhost');
define('DB_HOST', '');

That fixed the problem! :)

Friday, April 17, 2015

We can see the stars because Poynting vector is non zero

Do you ever look up at the night sky, and think "wow, these stars/planets are so far away from us, yet I can still observe them! How is that possible?!"

Chances are, you probably haven't.

Still, it is intriguing to think that we can potentially, given infinite time, observe a star/emitting body at the very end of the universe. This is all thanks to the non-zero Poynting vector in the equation for electromagnetic (EM) radiation.

I decided to write this blog post after my EM theory prof said "We can see stars because Poynting vector is non zero." I won't include any complicated theory or equations because 1) It's final exam season and I shouldn't even be writing this blog post and 2) you only need to know the basic concept.

What is a Poynting vector?
I assume you know what electric and magnetic fields are. (Electric fields are present when dealing with charged particles (like electrons), and magnetic fields when dealing with MOVING charged particles) Combine these fields, and you get an 'electromagnetic (EM) field'. These fields have a sense of direction about them, and depending on what you do with the field, you can get energy out of them. Poynting vector represents the directional rate of energy transfer of an EM field.

What is EM radiation?
Charges that are accelerating have EM fields that can transport energy "irreversibly out to infinity", and this is what we call "radiation." Given a charged particle that is accelerating in space, you can calculate the total power passing through its surface by integrating the Poynting vector. Clearly, this is non-zero if the Poynting vector is non-zero. But then, the EM 'news' travels at the speed of light, which means the energy left our charged particle at an earlier time. Have I lost you yet?

Think of it as pulling one end of a long slinky quickly. The other end of the slinky starts moving only after a certain amount of time. Now imagine that the slinky is 'energy', and you're moving it at the speed of light. (This might be an unfair analogy, since slinky expands while there is no sense of physical 'expansion' for energy)

Nonetheless, you measure the time at which the energy left the source (t0), and then measure another time point (t') when the energy crosses you at some other point in space, a distance 'r' away from the source. This means t' = t0 + r/c, where c is the speed of light. The power that is 'radiated' is essentially the amount of energy detected as r --> infinity. Obviously, since speed of light is constant, the further you move away from the source, the longer radiated energy will take to reach you -- but no matter how far away you are, it WILL reach you (even when there is a giant star between you and the source, thanks to gravitational lensing).

And this is precisely why we see stars!

UBC Course Review: EECE 360

Course: EECE 360
Topic: Systems and Control
Term: 2015W
Professor: Dr. Z. Jane Wang

Pre-reqs: EECE 202 or EECE 253 (Circuit Analysis II)

This was one of the core courses for engineering physics at UBC that I found most enjoyable and directly applicable. We got to learn about feedback system design, state-space analysis, root-locus method and frequency domain controller design. Course notes (ppt slide sets) were very useful in the beginning but lacked information for later chapters (especially for phase lead/lag design). Class attendance was decent (>50%), and most lectures consisted of ~20% theory explanations and 80% solving example problems. There were 5 major homework sets, due bi-weekly. Each took about 3 to 5 hours to complete, except for the "MATLAB assignment" which took about 8+ hours.

Overall, I would give the course 4.5 bode plots out of 5.

Disclaimer: These course reviews reflect my own personal views, which may differ from those of everyone else :o

Wednesday, March 25, 2015

Thoughts on Grad School (from Professors and Current Grad Students)

Today, I attended an interesting info session on grad school. There were talks from professors of physics and engineering, as well as from a current grad student.

I went in thinking that grad school wasn't really my thing, and came out reassured of that. :p Nonetheless, here is a list of recurrent topics during the session.

  • Things you need for grad school

    • GPA: If you are aiming for big name universities, you want a 88%+ overall average. Some students with 80% or above are considered, but only if they participated in extracurricular activities or they received high marks in the related field.
      • Comment: Given the insane workload (7 to 10 courses per term) of my program, this is quite hard to achieve (compared to 3 to 4 courses per term for other faculties). If you're in the same situation, read below, regarding reference letters.
    • Reference letters: Stellar, academic reference letters from possibly your undergrad research supervisor are the best, according to the grad committee member at the info session. If you haven't done undergrad research, a STRONG reference letter from a professor you frequently visit might work as well (with extra emphasis on strong!).
    • ! If your grades aren't as good, but you participated in various clubs, ask your referee to take that into consideration!
      • Comment: When asking your referees, give them at least two weeks to write, and always ask them if you could give them something to work with, such as a small blurb about what your previous experiences with your referee, or other important things you want mentioned in the letter. Remember, you won't be able to read the reference letter, so you want to give your referee as much information as you could that can help!
    • GRE, for American universities: You absolutely need to ACE the general GRE test, according to the director of my program. He has gotten 99th percentile on all subjects of his general GRE, but 60th percentile on the physics GRE, yet he still got into Stanford for masters in theoretical physics.

  • Pros and Cons of grad school

    • Pros:
      • You get paid to take courses and do your research
        • Never go to a grad school that requires you to pay!
      • You can take courses that you really enjoy
      • You have TIME to actually learn the material
        • In my current undergrad, it's honestly overwhelming to juggle 7 courses and thoroughly learn the materials.
    • Cons:
      • You don't get paid too much.
        • "You get to live just above the poverty line, enjoy Kraft Dinner, and share a basement suite with fun people"
      • You are pigeon-holing yourself in terms of knowledge
        • The professors had split opinions on this one. A physics professor gave many example cases where a student with a phD in one field got jobs in a completely different field, but with some overlap in terms of applied skills. Still, it seems true when they say you become the world-leader in that particular field, insofar as to add new knowledge to that field. This would indeed require a great deal of pigeon-holing..

  • Consider these points before applying for a grad school

    • If you are going to grad school so you can make more money, STOP
      • There is no guarantee that you will land a faculty job, or a job after your phD. Currently, there is an overflow of phD grads looking for placement. Faculty jobs are only possible for the top of the top students, and a "typical firm won't hire a phD student for a task that could be done by an undergrad". 
    • Don't go to grad school just because other people are going.
      • Make your own decisions! Consider everything, and do a LOT of research beforehand.
    • Don't be afraid to apply beyond the 'top universities'
      • Top universities might not necessarily be world-leading in your particular field of interest!

To give my two cents, grad school is indeed for people interested in becoming experts in their fields of interest. You should be willing to dedicate at least half a decade into it (after the 4 to 5 years of gruelling undergrad). Needless to say, if you are dedicated and work hard enough, you can definitely kick-ass, and you totally deserve that 'Dr.' prefix!