Journal

Quals

I passed both my Foundations and my AI qual.  I had to appeal for a rescore for my AI qual because the original grade showed that I failed.  Thankfully the regrade was accepted and I passed with the new score.

Now I passed all 4 of my exams: Foundations, AI, Compilers and Software Construction.  I believe I only have 2 more classes after this semester before I move on to having only to work on research.  I have a decent start with a thesis topic, Bounties.  Praise God.

Codebox

I found out about https://www.codebox.io/.  It is an online ide and it supports a ton of langs (including java).  It is open source, so you don’t have to use their services.  It also has desktop apps so you can work outside your browser.  The ide is customizable and you can make custom plugins etc.  Sounds awesome considering it is a two person company (a frontend and a backend dev).  I should see about setting it up.  I’ll probably try it out on their servers and if I really like it I’ll see about setting it up on my server.

Afternoon in DC

I went DC with David today.  Was fun.  We went to this Vegetarian festival (VegFest).  Was not as big as I thought it was going to be.  They had a variety of vendors and you could watch a 4min video (about animal cruelty and benefits of being a vegetarian) and make a dollar.  There was a guy at the entrance advertising “Fruititarian” I think he just made it up…  David couldn’t think of how you would get protein other than supplements.  They had fresh cut french fries, juices and a lot of Indian style food.  They had a whole section for dogs and dog food.  They even had a play area for dogs.  The festival was at Yards Park.  Not really the nicest park I have been too, certainly not as nice as the ones in Chicago.  It reminded me more of a parking lot than of a park.  No trees or grass just concrete.  A concrete park I guess…  One interesting thing was that on the walk to the park we saw this art installation inside a barn/warehouse like structure.  The art is hard to describe, but it made me think that probably that is what a big huge dinosaur’s backbone would look like.  Where instead of bone vertebrae it is a thousand molds of golden forearms making a fist.

We went to Park Tavern (aptly named since near Yards Park) to eat since it was close by the metro and the festival.  They have a very unique building with water fountains out front.  Google has some pictures.  Food was good, a bit expensive.

Had the idea that maybe revolving doors at the entrance into the train would allow people to get on and off faster during rush hour.  Not sure if it would work since it didn’t work so well when there was a bunch of people trying to get out of a burning building.

It is nice that I live close enough that I can just go into the city if I feel like it, but not have to deal with all of the bad traffic all the time.  Fairfax is bad enough.  Would be fun to go to the beach.  Maybe next year.

Microeconomics

I was learning a bit of micro to help my brother and here is a bit of what I learned.

The economics term for derivative is marginal.  Marginal revenue is the derivative of the revenue function.  Revenue is defined by R(q) = P(q)*q the price at a particular quantity times the quantity sold.  So, R'(q) = P'(q)*q + P(q) is the marginal revenue.  Usually P(q) does not change so P'(q) is zero. Therefore, R'(q) = P(q).  So, marginal revenue is the price I charged for producing one unit (remember P(q) is constant for any q).

Can also have marginal cost.  Which is similar to marginal revenue.

I also learned about elasticity.  Elasticity is the percent that Y changes in response to X changing by 1%.  In general elasticity is define by e = (dY/dX)*(X/Y).  This says the elasticity of Y with respect to X is the derivative of Y with respect to X times X over Y.  So, elasticity is a general thing you calculate for anything.  You just plug the words in for Y and X.  For example, the elasticity of demand with respect to price is: n = (dQ/dP)*(P/Q).  However, the demand curve usually has a negative slope so the derivative is negative.  Economists don’t like the negative so they usually write the elasticity of demand as n = -(dQ/dP)*(P/Q).  Remember D'(p) = (dQ/dP) and D(P) = Q = some equation in terms of P.  Usually, we like our equations to be in terms of one variable so I would substitute like this: n = -(dQ/dP)*(P/D(P)).  So, what does elasticity of demand tell us?  Well, first demand tells us how much a consumer buys at a particular price.  Elasticity looks at how the quantity changes as price changes.  So, 0<=n<1 if the demand for a good at that price is inelastic.  Meaning the quantity demanded doesn’t change radically.  If n > 1 then the demand is elastic meaning if we change the price the demand will change quite a bit.

Another interesting thing I learned was about the market demand residual.  This starts to be interesting because it is taking into account other (possibly identical) businesses.  The market demand residual is defined as Dr(P) = D(P) – So(P) where So(P) is the supply of all the other businesses that are identical and D(P) is the demand of the business that is being examined.  So, if there are n identical business then So(P) = sum(i = 1 to n-1) of Si(P).

Proof that the counting subset sum is in #P (Sharp P)

Yesterday I gave a presentation proving that in theory group.  Presenting a proof is a lot harder than it seems when proving it to yourself on paper.  Suggestion for presentations in the future: say what I am going to do then write it up on the board.  Then after writing point to the different equations that I had previously explained.  Here are some of the lecture notes that I used to prepare.