Visualize, 2

Posted on October 7, 2022 by rpflee

visual

~ spatial

~ global

~ parallel

Since our retinas are 2D, what we see are actually only 2D.

— Me@2016-08-20 03:11:13 PM

The point is not to eliminate risk,

Posted on October 7, 2022 by rpflee

but to minimize risk

~ take the best kind of risk

~ aka FAITH.

— Me@2017-01-04 11:03:09 PM

What is a leader? 2

Posted on October 6, 2022 by rpflee

Presentation 基本原理 1.2.2.4

這段改編自 2010 年 4 月 24 日的對話。

When You’re Teaching a Subject, Don’t Think About That Subject: Think About Teaching – don’t focus on subtleties that interest you; focus on your audience.

— How to Teach Stuff

— John Baez

第二個重點教學原則是：

Focus on teaching, not the subtleties that interest you.

即是聚焦於教學成果，而不是你最有興趣的細節。

亦即是話，重點不是「你」，亦不是「觀眾」；重點是「教學」本身。

教學時候，你應該說的，既不是你想說的，亦不是觀眾想聽的。

（安：難道什麼也不說嗎？）

不是這個意思。

教學時候，你應該說的是，既不是你想說的，亦不是觀眾想聽的，而是觀眾需要的。

假想你是醫生，你想說給病人的，就是光顧最昂貴的療程；病人想聽的，就是他其實沒有大礙，什麼針藥也不需。但是，它們兩者，也不是你應該講的。

不是以你為中心，亦不是以觀眾為中心，而是以原則為中心。

「以原則為中心」對我來說，是新知識。我以前一直以為，不以自己為中心，不自說自話，改為講「觀眾想聽」的，就已經正確。但是，我漸漸地發現，只講「觀眾想聽」的，又好似有些問題。

（安：教學就是令人，愚蠢變聰明。原本愚蠢的人，很難會知道當刻學什麼，對智力最有利。）

A good leader tells you not what he wants to say, not what you want to hear, but what you need to know.

— Me@2022-10-05 10:23:24 AM

Euler problem 4.1

Posted on October 3, 2022 by rpflee

(describe #'elt)

(defun palindromep (seq)
  (let ((end (1- (length seq))))
    (or (< end 1)
        (and (eql (elt seq 0) (elt seq end))
             (palindromep (subseq seq 1 end))))))

(defun euler-4 ()
  (loop for a from 1 to 999
      maximize
      (loop for b from 1 to 999
            when (palindromep
                    (prin1-to-string (* a b)))
              maximize (* a b) into best
            finally (return (or best 0)))))

— skeeto/euler-cl

— Me@2022.10.03 03:03:30 PM

3.2 Maxwell equations in four dimensions, 2

Posted on October 2, 2022 by rpflee

A First Course in String Theory

(b) Show explicitly that the Maxwell equations with sources emerge from (3.34).

~~~

Eq. (3.34):

$\displaystyle{\begin{aligned} \frac{\partial F^{\mu \nu}}{\partial x^\nu} &= \frac{1}{c} j^\mu \\ \end{aligned}}$

$\displaystyle{\begin{aligned} \frac{\partial F^{\mu 0}}{\partial x^0} + \frac{\partial F^{\mu 1}}{\partial x^1} + \frac{\partial F^{\mu 2}}{\partial x^2} + \frac{\partial F^{\mu 3}}{\partial x^3} &= \frac{1}{c} j^\mu \\ \\ \end{aligned}}$

$\displaystyle{\begin{aligned} \frac{\partial F^{0 0}}{\partial x^0} + \frac{\partial F^{0 1}}{\partial x^1} + \frac{\partial F^{0 2}}{\partial x^2} + \frac{\partial F^{0 3}}{\partial x^3} &= \frac{1}{c} j^0 \\ \frac{\partial E_x}{\partial x^1} + \frac{\partial E_y}{\partial x^2} + \frac{\partial E_z}{\partial x^3} &= \rho \\ \nabla \cdot \mathbf{E} &= \rho \\ \\ \end{aligned}}$

$\displaystyle{\begin{aligned} \frac{\partial F^{1 0}}{\partial x^0} + \frac{\partial F^{1 1}}{\partial x^1} + \frac{\partial F^{1 2}}{\partial x^2} + \frac{\partial F^{1 3}}{\partial x^3} &= \frac{1}{c} j^1 \\ - \frac{\partial E_x}{\partial x^0} + \frac{\partial 0}{\partial x^1} + \frac{\partial B_z}{\partial x^2} - \frac{\partial B_y}{\partial x^3} &= \frac{1}{c} j^1 \\ \frac{\partial B_z}{\partial y} - \frac{\partial B_y}{\partial z} &= \frac{1}{c} j^1 + \frac{\partial E_x}{\partial x^0} \\ \end{aligned}}$

— Me@2022.10.02 11:49:59 AM

For all, 10

Posted on October 1, 2022 by rpflee

No observer can observe and get all the information of the current state of the whole universe.

Since the definition of the “universe” is “everything”, any observer must be part of the universe. Also, in the universe, any observer has at least one thing it cannot observe directly—itself.

Therefore, no observer can observe the whole universe in all details.

— Me@2022.09.30 07:57:46 PM

Can a part of a painting represent all the information of the whole?

No.

(Kn: Yes, if excluding itself.)

That is exactly my point.

“Yes only if that part does not contain that part itself” is equivalent to “no”.

— Me@2016-08-20 03:30:26 PM

Physics Town

continues

Monthly Archives: October 2022