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Lewis Carroll – computing the day of the week for any given date (1887)

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Re: Lewis Carroll – computing the day of the week for any given date (1887)

#41

Post by jrochkind1 »

jihadjihad wrote: post #6
ColinWright wrote: post #3

This is very similar to the method I use and, after conversation with him, the method Art Benjamin uses. It's trivial to do in 10 to 15 seconds, though it requires practice, a very small amount of memorisation[0], and a small amount of mental arithmetic. I use it regularly, partly to keep in practice, and partly because once you have the skill you find it's surprisingly useful. JH Conway used a different technique[1]…

> which I have swutch to That's a past participle I've never seent before

For some reason part participles are particularly hard for me too (native English speaker who speaks no other languages fluently). (they must just be a mess in English? I can't imagine how non-native speakers ever get any of them)

I'm going to go with swutcheted

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#42

Post by rrgmitchell »

thyrsus wrote: post #37

I'm having trouble following the algorithm for the month number. From the article: The Month-Item. — If it begins or ends with a vowel, subtract the number, denoting its place in the year, from 10. This, plus its number of days, gives the item for the following month. The item for January is ‘0’; for February or March (the 3rd month), ‘3’; for December (the 12th month), ’12.’ [So, for clarity, the required final numb…

I struggled with this too. The best understanding I've been able to come to is this:

1. Every month's item number can be calculated from the preceding month's item number by the method given. I.e. add the number of days in the preceding month to the preceding month's item number then take mod 7.

2. For January we take it that there is no preceding month. Therefore the numbers in such a calculation are all zero, so we end up with zero.

3. For later months you don't need to start at January and go month by month to the month you want; you can start at a month with a start- or end-vowel and use the shortcut that such a month's item number is ten minus the month number.

4. For the purposes of 3, 'y' does not count as a vowel.

Or maybe it's easier just to learn them!

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#43

Post by omoikane »

throwaway211 wrote: post #4

Reading the article, I wandered into the difference of Old Style and New Style dates and what happened in 1752. From [1]: By the 18th century, the English legal year – used for legal, financial and other civil purposes – had for centuries begun on 25 March, or Lady Day.[13][i] Thus, for example, 24 March 1707 was immediately followed by 25 March 1708, while the day following 31 December 1708 was 1 January 1708, with…

The linux `cal` utility has special handling to recognize September 1752:

https://github.com/util-linux/util-linux/blob/9f15d2de811773...

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#45

Post by andyjohnson0 »

throwaway211 wrote: post #4

Reading the article, I wandered into the difference of Old Style and New Style dates and what happened in 1752. From [1]: By the 18th century, the English legal year – used for legal, financial and other civil purposes – had for centuries begun on 25 March, or Lady Day.[13][i] Thus, for example, 24 March 1707 was immediately followed by 25 March 1708, while the day following 31 December 1708 was 1 January 1708, with…

To this day the UK tax year still begins on April 6th, for reasons [1] that have to do with the migration from Julian to Gregorian calendars almost 300 years ago. I wonder if other countries have so many of these legacy patches from ye olden times.

[1] https://theconversation.com/why-the-uk-tax-year-begins-on-ap...

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#46

Post by tzs »

llm_trw wrote: post #22

To people who say that notation doesn't matter, this is what all mathematics was like before we got our new better notation. I'd go as far as saying that in mathematics little other than notation matters and the same is true in computer science. This is why lisp like languages are the obvious choice when variables are explicit.

Chess was like that too. Consider a game where the first move was for white to move the knight that is closest to the white king to the square that is two squares forward and one square to the left of where the knight started.

Here's how that move would have been written at various times from the 17th century to the present [1].

Early 1600s: The white king commands his owne knight into the third house before his owne bishop.

Mid-1700s: K. knight to His Bishop's 3d.

Early 1800s: K.Kt. to B.third sq.

Around 1850: K.Kt to B's 3rd.

Around 1860: K.Kt to B. 3d.

Around 1870: K.Kt to B3.

Around 1890: KKt-B3.

Early 1900s: Kt-KB3.

Mid 1900s: N-KB3.

Last quarter of 1900s to present: Nf3 or if you want to avoid language-specific piece names ♘f3.

[1] https://www.knightschessclub.org/the_history_of_notation.htm...

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#47

Post by digging »

SamBam wrote: post #25

So Lewis Carroll's method for today (May 24 2024): The Century-Item: The year is 2024. The century is 20. 20/4 = 5, with no remainder. Overplus is 0. 3-0 = 3. 3x2 = 6. The Year-Item: The year part is 24. Number of dozens: 2 24/12=2. Overplus: 24 mod 12 = 0. Number of 4's in the overplus: 0. 2+0+0 = 2. The Month-Item: May: 1 (from the text). The Day-Item: The day is 24. Adding all items: 6+2+1+24=33. 33 mod 7 = 5, whi…

> The Month-Item: May: 1 (from the text).

This was the part I as hoping you'd write out :) I can't make heads or tails of the explanation.

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#48

Post by v8xi »

thyrsus wrote: post #37

I'm having trouble following the algorithm for the month number. From the article: The Month-Item. — If it begins or ends with a vowel, subtract the number, denoting its place in the year, from 10. This, plus its number of days, gives the item for the following month. The item for January is ‘0’; for February or March (the 3rd month), ‘3’; for December (the 12th month), ’12.’ [So, for clarity, the required final numb…

Also had this issue. I even tried a bunch of different reformulations/reinterpretation of the provided formula and nothing helped :(

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#49

Post by cyberax »

jrochkind1 wrote: post #41
jihadjihad wrote: post #6

Earlier quoted context omitted.

> which I have swutch to That's a past participle I've never seent before

For some reason part participles are particularly hard for me too (native English speaker who speaks no other languages fluently). (they must just be a mess in English? I can't imagine how non-native speakers ever get any of them) I'm going to go with swutcheted

English verbs are pretty tame compared to Slavic verbs that can be modified with all kinds of perfective prefixes.

On the other hand, Chinese verbs are even easier. They don't even have a tense!

Re: Lewis Carroll – computing the day of the week for any given date (1887)

#50

Post by rhdunn »

thyrsus wrote: post #37

I'm having trouble following the algorithm for the month number. From the article: The Month-Item. — If it begins or ends with a vowel, subtract the number, denoting its place in the year, from 10. This, plus its number of days, gives the item for the following month. The item for January is ‘0’; for February or March (the 3rd month), ‘3’; for December (the 12th month), ’12.’ [So, for clarity, the required final numb…

January -- The item for January is ‘0’ = 0

February, March -- The item ... for February or March (the 3rd month), ‘3’ = 3

December -- The item ... for December (the 12th month), ’12.’

So these all use fixed values.

The `(10-place)+days mod 7` logic works for May, July, September, and November using the previous month's values -- effectively every other month. The vowel trick is likely a nmemonic for not having to remember which months to do this for.

The other months are the previous month's `item+days mod 7`, although it is unclear where this interpretation is deduced. -- The "If it begins or ends with a vowel, subtract the number, denoting its place in the year, from 10." text does not apply, so I would have assumed that is was 0 not the calculated item value. Thus, I would have expected it to just use the days in month.

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