Essential Mathematics for Economics

Round trip between San Diego and Atlanta

less than 1 minute read

Published: October 13, 2025

I often fly bewteen San Diego and Atlanta, usually with Delta (because there are more flight options than Alaska, which also offers direct flights between SAN and ATL). As I was looking to book my next trips, I noticed that flight tickets got much more expensive, often over $600 round trip with Delta (main cabin). After playing around with various searches, I realized that if I book a round trip from Atlanta instead of from San Diego, the price drops by 25% or more. I am not sure why, but maybe it’s because if I book from Atlanta, the trip is over the weekend, so the booking system may judge myself as a (price-sensitive) leisure traveller. By using Alaska instead of Delta, the price often drops below $300 round trip. Although I have achieved gold status with Delta, since Alaska is much cheaper and also offers status match, I will likely switch.

Econ Journal Watch goes LaTeX

less than 1 minute read

Published: September 30, 2025

Great news. Starting from the September 2025 issue, Econ Journal Watch publishes papers typeset in LaTeX.

For years, I have been begging the editorial board of EJW to accept LaTeX submissions. This summer, I attempted to submit a comment to urge EJW to accept LaTeX submissions, but to my surprise, I was told EJW was working to transition to LaTeX over the summer, so the point of my comment became moot. The call for papers does not seem to be updated yet, but we will see whether they will officially announce that they welcome LaTeX submissions.

American Express increased annual fee of Platinum Card to $895

3 minute read

Published: September 20, 2025

American Express increased the annual fee of Platinum Card from $695 to $895.

In this post last year, I discussed my love-hate relationship with the American Express Platinum Card. When I opened the account many years ago, I recall that the annual fee was $450. Then it increased to $550 and then to $695. Now it’s $895. It has increased to the point that I need to reconsider whether it is worth keeping the card. (See also this opinion.)

The card provides various credits, but most of them are things that I won’t use or are redundant.

• $400 Resy credit ($100 quarterly): Most of the restaurants that I go anyway (Asian food) are not in Resy. To me, it makes most sense to use Resy restaurants for business (for which I get reimbursed) and get the credit, but optimizing is a mental burden.
• $600 Hotel credit ($300 semi annually): This is for Fine Hotels + Resorts or Hotel Collection, and you need to stay for two nights. Most hotels are expensive. If I can use it for business trips (for which I get reimbursed), it is worth it, but I won’t stay at these hotels for personal trips.
• The American Express Global Lounge Collection: This is a benefit I have valued in the past (to get free food, drinks, and space at airports, especially Centurion Lounges). But now that I achieved Delta Gold status (I also have One World Emerald status), its value has declined relatively.
• $200 Uber credit: This is useful when I travel. During off-season, I have to use it for Uber Eats. (Uber Eats is overpriced to begin with, so I usually order one Indian curry for pick up on Uber Eats and then order extra stuff at the restaurant directly.)
• $120 Uber One Credit ($10 monthly): The cost of Uber One is $9.99 per month, so essentially it’s free. I have just signed up for this service so I will see whether it’s useful.
• $300 Digital Entertainment Credit ($25 monthly): This is useless. I don’t use these kinds of services.
• $200 Airline Fee Credit: I use it for Delta, and in the past it helped me cover change fees or upgrades. But it’s not really necessary.
• $209 CLEAR Plus credit: CLEAR used to be useful for skipping the security line at the airport. But TSA Precheck has improved (with digital ID, etc.) and I no longer see value in CLEAR.
• Hilton Honors Gold Status: You get free breakfast for two people, but I rarely stay at Hilton.
• Marriott Bonvoy Gold Elite Status: I have a different Marriott card, so this is redundant.
• Leaders Club Sterling Status from The Leading Hotels of the World: I have never heard of this hotel chain.
• Fee Credit for Global Entry or TSA PreCheck: This is useful, but I have two other cards that provide the same benefit, so it is redundant. (I can use for family members, though.)
• $300 Lululemon credit ($75 quarterly): My wife and daughter buy stuff at Lululemon sometimes, so it could be useful.
• $100 Saks Fifth Avenue credit ($50 semi annually): I won’t shop at Saks unless there is this credit. I just buy minimal stuff like underwear that are on sale.
• $200 Oura Ring credit: I don’t know what this crap is.
• Walmart+ Monthly Membership credit ($12.95 monthly): I don’t use it.

I didn’t list all the benefits and credits, but the rest are less important. My membership renewal is next May, so I still have time to think about it.

Slavery descendants to get preference for college admission if bill approved

less than 1 minute read

Published: September 17, 2025

This is insane. The California Assembly Bill 7 states

This bill would state that the California State University, the University of California, independent institutions of higher education, and private postsecondary educational institutions may consider providing a preference in admissions to an applicant who is a descendant of slavery, as defined, to the extent it does not conflict with federal law.

As a classical liberal, I believe that whether you should be admitted to college or not depends only on your merit, and who your ancenstors were has no relevance. Besides, how do you even verify whether one of your ancestors was a slave?

The radical left have often promoted discrimination under the name of DEI. This one has the same intention, although it is carefully worded (“may consider providing a preference […] to the extent it does not conflict with federal law”) so that it is not legally binding.