Blog on Xingyu Chen

Comparative Civilisation Economics: The Robot Civilisation

Thu, 14 May 2026 00:00:00 +0000

“The robot civilisation has the simplest economic structure of all the descendant civilisations we know of. Its simplicity is not because it is primitive, but because its creators — us — removed for it almost all the conditions that make economics necessary.”

— Outline of Comparative Civilisation Economics, Chapter 2

Origins

Lately I have been reading Mankiw’s Principles of Economics as bedtime reading, and I began to imagine: what are the civilisation-level assumptions on which the various concepts and phenomena of economics depend? If we switched to a different form of civilisation, would the whole set of basic economic concepts and phenomena — prices, markets, money, finance, employment, inflation — still arise?

The Endless Surge

Tue, 12 Nov 2024 23:42:00 +0800

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The tune that has been stuck in my head lately is California Dreaming. The confused, clamorous period is finally over. The American-style fantasy of a life — growing wild, lurching left and right, never resting, never at peace, wandering everywhere — seems to be coming to an end. In the end you have to face a long, boundless life: a Cthulhu-like leviathan you have never once given your serious attention.

Mathematica Pitfalls: Symbolic Matrix Computation

Fri, 17 Mar 2023 18:34:35 +0800

Where the problem came from

Lately, in order to derive some formulas, I needed to verify the inner-product results of a number of high-dimensional matrices (more than twenty of them, each taking anywhere from one to eight hours by hand), and I needed a reliable tool to help me check my computations. So I thought of Mathematica.

My computation was roughly this: take two $k^2\times k^5$ matrices $A,B$ and compute their inner product $Tr(A \cdot B^T)$. Using the cyclic property of $Tr$, this can be turned into a sort of “inner product” between a $1 \times k^2$ row vector, a $k^2\times k^5$ matrix and a $k^5\times 1$ column vector — that is, adding up a pile of ($k^2\times k^5$) numbers. But $A$ and $B$ are not scalar matrices: their entries are all symbolic, and the dimensions grow with the order of the formula.

My Intellectual Diet

Sat, 12 Nov 2022 01:46:35 +0800

Over lunch I watched Ma Dugong’s “Bedtime News” #440, “Took Ten Years to Revise — Who Actually Cares About Textbooks?”, and it left me with some thoughts. I posted them in the show’s comment section and sent them as a direct message.

I was born in 2001 in a village in Henan. I did primary and middle school in the countryside, moved to the county town for high school, and I am now a third-year undergraduate at HUST, on the science track. I want to share some of my experience. My father was born in 1968 and my mother in 1966; both finished middle school but never went to high school. My father was a good student, but the family had no money and my grandparents did not care. He was also going through a rebellious phase, and figured that if he was not going to school, then so be it — though he has plenty of regrets now, and when I was in high school he would often pour his heart out to me after he had been drinking. My mother stopped for the same reason — no money — and also because her mother fell seriously ill and needed looking after. Still, my parents took my education very seriously. Their main concern was simply that I should not stay in the village or end up doing nothing but manual labour, though my father had higher hopes than that. Ultimately, he wanted me to fly out, to see the wider world, and not to be boxed in by a small village.

Three Years of Course Reviews at the HUST School of Mathematics

Mon, 25 Apr 2022 18:34:35 +0800

This piece was written in the second semester of my third year, in response to a survey by Professor Yan Kai soliciting opinions on how the school trains its students. Professor Yan wanted us to speak our minds plainly. Some of the evaluations may be somewhat intemperate, but they more or less reflect my state of mind and understanding at the time. The evaluations are for reference only.

The first three semesters

Mathematical Analysis

Teacher: Tang Yanbin (first semester), Huang Yongzhong (second and third semesters), Zeng Haozhi (problem sessions) Textbook: Cui Shangbin. Time: from first year through the first semester of second year, three semesters in total Evaluation: Both teachers were very conscientious. Professor Huang put a lot of care into it and would hand out plenty of supplementary material. I used to fire away at Cui Shangbin’s textbook and told every junior I met to switch to another book, but now I can genuinely appreciate Professor Huang’s good intentions — a textbook with no answers really does matter. At the beginning, the theory of the real numbers was hard to accept, and I think the main issue was the logical starting point: we had not yet realised where the logical starting point lay. We could accept that one had to begin with the real numbers, but it was not clear why it had to be made so complicated. It was all a muddle. As I went deeper into mathematics and my logical training deepened, though, I stopped worrying about it — it really does have to be done this way. One complaint, though: the problem sessions were not very effective. As a beginner there was a great deal I was muddled about, and once the teacher went a little deeper I simply could not follow. It would have been better to concentrate on going through the homework. In the second semester of first year, when classes were online, the teacher would post the homework solutions, and I actually think that was when the problem sessions helped most.