IEEE 也宣佈禁用 Lenna 圖了

Lenna (Lena) 是個經典的標準測試圖片,一方面是因為有很多細節可以觀察 image-related algorithm 的情況,另外一方面也是因為這張圖是取自 1972 年的 Playboy 雜誌:

Lenna (or Lena) is a standard test image used in the field of digital image processing starting in 1973, but it is no longer considered appropriate by some authors.

To explain why the image became a standard in the field, David C. Munson, editor-in-chief of IEEE Transactions on Image Processing, stated that it was a good test image because of its detail, flat regions, shading, and texture. He also noted that "the Lena image is a picture of an attractive woman. It is not surprising that the (mostly male) image processing research community gravitated toward an image that they found attractive."

也因為後者的原因,後來也有愈來愈多其他的圖片可以達到類似的效果 (甚至更好),就有替代的聲音出現了。

另外一方面,Lena 本人在 2019 年也提到希望淡出的想法:「How a Nude “Playboy” Photo Became a Fixture in the Tech World」。

But I retired from modeling a long time ago. It’s time I retired from tech, too.

而最新的消息就是 2024/04/01 開始,IEEE 不再接受使用 Lenna 圖的投稿:「Institute bans use of Playboy test image in engineering journals」。


用 PageRank 跑 arXiv 上面 CS paper 的排名

在「Ask HN: AI/ML papers to catch up with current state of AI?」這邊看到的,本來只是在討論有哪些 AI/ML paper 可以看,結果在 id=38654200 這邊看到這個網站,上面的資料是每天更新一次:

This tool can help you find what's new & relevant to read. It's updated every day (based on ArXiv).

You can filter by category (Computer Vision, Machine Learning, NLP, etc), by release date, but most importantly, you can rank by PageRank (proxy of influence/readership), PageRank growth (to see the fastest growing papers in terms of influence), total # of citations, etc...

依照「Frequently Asked Questions」的說明,是用 PageRankarXiv 上面的 paper,主要是 CS 為主。

難得看到 PageRank 出現而且是用在 paper citation 上面...


Hacker News Daily 上看到「“You don't have a voltmeter. Do you have a potato?” (」這則討論,原討論在「Is white wire with grey stripes positive or negative wire?」這邊,有人問了一個問題,說手上有一個交流轉直流的變壓器,想要重新接線到下面這種端子,但不確定變壓器輸出的兩條線裡面,正極與負極分別是哪條:

下面的答案很厲害啊,開頭先說如果你沒有伏特計 (像是三用電錶),那手上有沒有馬鈴薯:

You don't have a voltmeter. Do you have a potato?

把馬鈴薯切半,把 DC 端的兩條線插到同一顆馬鈴薯上面,大約相距 2cm,插電不久後就可以看到有一端會變綠,那端就是正極,把本來插到馬鈴薯上的端子剪掉後再接線就可以了:

With the power adapter unplugged from your electrical outlet, cut the wires, strip a little insulation from the ends, twist the strands of each wire into a point. Do not allow the bare wires to touch each other from this point on.

Cut the potato in half. Take one half, and poke both wires into the cut face of the potato about 2 cm apart. Plug in the power adapter to the wall outlet. In a short time, the potato around one of the wires will turn green. That is the positive wire.

Unplug the adapter and clip off the ends of the wires so you have clean wire for soldering your new plug.

不確定產生的是不是銅綠,但能給出這種解法的確很有娛樂性 XDDD

Fred Brooks 過世

Hacker News Daily 上看到的消息,Fred Brooks 過世了:

Hacker News 上的討論在「Fred Brooks has died (」這邊可以翻。

Fred Brooks 是 1999 年的 Turing Award 得主:

For landmark contributions to computer architecture, operating systems, and software engineering.

不過在電腦軟體產業裡,用他另外一個被廣為人知的作品來介紹會比較快,軟體工程的經典書籍「人月神話 (The Mythical Man-Month) (MMM)」的作者,從 Hacker News 的討論串裡面也可以看到很多對 MMM 的討論。

Starlink 想要在太空直接提供 5G 網路訊號讓地面手機使用

Hacker News 上看到 Starlink 打算跟 T-Mobile 合作,直接用衛星提供 5G 訊號讓地面手機使用:「SpaceX, T-Mobile to connect satellites to cellphones in remote areas (」,原報導在 WSJ 的「SpaceX, T-Mobile to Connect Satellites to Cellphones in Remote Areas」這邊,另外因為 paywall 的關係,可以在這邊讀。


Mr. Musk said the service would use second-generation Starlink satellites that would be outfitted with large antennas that cover swaths of land that have no service. SpaceX has a pending application before the FCC to launch around 30,000 of the second-generation satellites over time.

在另外一篇報導「SpaceX and T-Mobile team up to use Starlink satellites to ‘end mobile dead zones’」裡面有提到更細一點,不是衛星電話,是目前一般的手機:

The service won’t require mobile users to get a new phone. Musk said in or after a natural disaster, even if all the cell towers are taken out, the planned service should work.

不過可以預期只會有很基本的服務 (大概確保通話與簡訊會通),針對緊急危難狀況會特別有幫助:

Mr. Musk said that the bandwidth would be limited and that the new satellite service wouldn’t supplant existing ground-based cellular services. “This is meant to provide basic coverage to areas that are completely dead,” he said.

翻了翻 wiki,目前 Starlink 第一代衛星的軌道高度是 340km 左右,好像還不確定二代衛星會在哪個高度...

Hacker News 上有蠻多人在算技術上的可行性,除了訊號強度外,衛星與地面相對速度比目前地面上的交通工具都快,都卜勒效應 (Doppler effect) 看起來也是個會影響很多的主題...

不過討論裡面有提到 2021 年就已經有其他商用公司在幹類似的事情,所以看起來不只是講講而已?應該是有些可能性:「Lynk demos global satellite connection for ordinary phones and prepares for commercial launch」。


一樣是 Hacker News 上看到的:「Guidance to make federally funded research freely available without delay (」,白宮的公告在「OSTP Issues Guidance to Make Federally Funded Research Freely Available Without Delay」這邊。

開頭有重點,不得限制以及收費。所以 paywall 是一定不行,另外要註冊才能看也算是一種限制,應該也會被這次的政策要求改善:

In a memorandum to federal departments and agencies, Dr. Alondra Nelson, the head of OSTP, delivered guidance for agencies to update their public access policies as soon as possible to make publications and research funded by taxpayers publicly accessible, without an embargo or cost.

時間表的部份,短期是 2023 年中更新 policy,並且在 2025 年年底前全部施行:

In the short-term, agencies will work with OSTP to update their public access and data sharing plans by mid-2023. OSTP expects all agencies to have updated public access policies fully implemented by the end of 2025.


找了一下之前寫下來跟 open access 有關的消息,從學校方面給壓力的也不少,不過我記錄下來的主要都是跟 Elsevier 的中止合約:


Banner blindness

前幾天的 Hacker News Daily 上看到「Why do people not notice our enormous, prominent, clear and contrasting purple banner?」這篇 2018 年的討論,裡面在講為什麼使用者會常態性忽略 banner 的內容。

在答覆區裡面有人提到了維基百科上面的 Banner blindness 這個條目,題到了網站的使用者會刻意或是非刻意的忽略掉像 banner 的資訊:

Banner blindness is a phenomenon in web usability where visitors to a website consciously or unconsciously ignore banner-like information. A broader term covering all forms of advertising is ad blindness, and the mass of banners that people ignore is called banner noise.

開頭也提到了 banner 廣告 CTR 的變化:

The first banner ad appeared in 1994. The average click-through rate (CTR) dropped from 2% in 1995 to 0.5% in 1998. After a relatively stable period with a 0.6% click-through rate in 2003, CTR rebounded to 1% by 2013.



Hacker News Daily 上看到的,原文標題比較漂亮:「Car Seats as Contraception」,在 Hacker News 上也有討論:「Car seats as contraception (」,重點是作者之一 (David H. Solomon) 也有跑上去回應。

Abstract 的部份把重點都講出來了,1977 年美國通過汽車的兒童安全座椅法律,但大多數的汽車無法放下第三張座椅,這反而使得生第三胎的成本大幅提高 (需要買空間更大的車),然後另外拉出資料分析因為法律而制止的車禍數量:

Since 1977, U.S. states have passed laws steadily raising the age for which a child must ride in a car safety seat. These laws significantly raise the cost of having a third child, as many regular-sized cars cannot fit three child seats in the back. Using census data and state-year variation in laws, we estimate that when women have two children of ages requiring mandated car seats, they have a lower annual probability of giving birth by 0.73 percentage points. Consistent with a causal channel, this effect is limited to third child births, is concentrated in households with access to a car, and is larger when a male is present (when both front seats are likely to be occupied). We estimate that these laws prevented only 57 car crash fatalities of children nationwide in 2017. Simultaneously, they led to a permanent reduction of approximately 8,000 births in the same year, and 145,000 fewer births since 1980, with 90% of this decline being since 2000.

濃濃的政治不正確感 XD

證明圓周率 π 是無理數

前陣子在 Michael Penn 教授的 YouTube 頻道上看到的證明:

這個證明方式在其他人的 YouTube 頻道也有做過,像是 MindYourDecisions 在 2019/3/14 (Pi Day) 發表的影片:

這兩篇使用的方法是 Ivan M. Niven 在 1946 年提出來的方法 (發表在 1947 年 AMS 的期刊,第 53 期的 Bulletin of the American Mathematical Society 上):「A simple proof that π is irrational」。

先不討論證明方法本身,我把這份 PDF 印出來慢慢看,當年用打字機打的字型讀起來超有味道的... (這份 PDF 看起來是掃描檔)

從 PDF 可以看出證明超級短,只有一頁,但畢竟這是大師丟出來的證明,裡面其實省了很多步驟。這接步驟不難推導,但是是屬於考試作答時不能省略的部份,如果加上去的話應該會兩到三頁 (還是非常短)。


\frac{d}{dx} sin(x) = cos(x)\newline\newline\frac{d}{dx} cos(x) = -sin(x)


\frac{d}{dx} f(x)g(x) = f'(x)g(x) + f(x)g'(x)

積分的部份只用了定義的部份 (主要是在微分的部份證完)。

然後證明是圍繞在「整數」上面做文章,夾擠出一個不可能的情況,因此得到矛盾,證明了 π 是無理數。

整個證明可以在高三範圍 (如果現在高三還有教微積分的話) 或是大一教過微積分之後的程度證完,作者講的 "Simple" 主要是出自這邊...

第四堂:「Data Wrangling」


這個系列是從『MIT 的「The Missing Semester of Your CS Education」』這邊延伸出來的,這邊講的是「Data Wrangling」這篇。

這篇是在講 pipe 的用法,在講這些工具之前,其實有個很重要的概念應該要說明 (但沒有在這篇文章裡被提到),也就是 Unix philosophy,這個哲學是指 unix 環境下的工具,都會設計成只做好一件事情。

而要怎麼把這些工具串起來,最常見的就是 pipe,你可以在文章裡看到 grepsedsort 這些工具的用法,以及怎麼用 pipe 串起來。

這邊剛好也可以提一下,利用 pipe 可以把不同功能打散到不同的 process 上,剛好也可以稍微利用到現在常見的多 CPU 的環境。

另外上面因為提到了 grep,文章內花了不少篇幅在講 Regular expression 這個在 CS 課程裡面也是重要的基礎。

會放這種篇幅長度,一方面是 Regular expression 的實用性很高,另外一方面,學術上與自動機理論中的 DFANFA 都有關,算是學習計算理論的起點:

然後後面就有提到 AWK 這個工具,這邊要注意的是,雖然可以用 Perl 之類的工具作到類似的事情 (而且更強大),但 AWK 有被放到 POSIX 標準裡,所以在各種作業系統內幾乎都一定會出現,加上語法算是簡單,學起來還是很有幫助...

然後再最後面的段落冒出一個 gnuplot 畫個圖,以及示範 xargs 這種神器要怎麼用 (這邊會更建議看一下 manpage,可以配合 find 之類的工具用,並且平行化同時處理)。

然後最後示範了 binary data 怎麼處理。