/sci/ - Science & Math

Hello /sci/ I must be developmentally challenged because I can't understand modulus

When it comes to modulus I always assumed it was like an integer remainder operator.

i.e. 5%10 = 5 because 5/10 = 0 r 5
and 5%3 = 2 because 5/3 = 1 r 2

When it comes to negatives I just can NOT grasp the concept

-5%7 isn't -5 and instead gives 2
-4%3 isn't -1 and instead gives 2 as well

I can rationalize the first example by turning off my brain and just adding the second and the first together, but it doesn't apply to the bottom, and I KNOW that's not how it really works.

I came across this problem when looking at how to improve and shorten rock paper scissors code in python. I can make a seperate post with that snippet, but what's really important here is that I'm FUCKING STUPID and don't understand how modulus REALLY works especially with negatives.

Explain it to me like I'm fucking dumb because I am /sci/

HOW DOES MODULUS WORK WITH NEGATIVES?

I always thought of modulus as a remainder operator i.e. 5 % 10 would be 5 because 5/10 in integer division is 0 with a remainder 5. 5 % would be 2 because 3 goes into 5 once with a remainder of 2 etc. etc.

When it comes to negatives I get completely lost.
-5 % 3 in my mind would give -2, but it gives 1.

-3 % 7 in my mind would give -3 for the above reason but it's instead 4. The only way I can wrap my head around it is if I just subtract the first from the second, if the second is larger and the first is negative, but I KNOW this isn't how it works.

I came across this problem while looking at a solution for simplifying a rock paper scissors script in python using dictionaries and keys.

I didn't understand how or why modulus could be used to eliminate all the conditionals and relegate it to one line to determine whether user input won.

tl:dr How does modulus actually work with negative numbers? I can't understand the actual reason, even though I know a brain dead solution.

Hey Guys!

Need some help trying to work out a formula to return a percentage

Basically I'm trying to compare two football teams based on a bunch of statistics to then predict who would win in a game.

One of the statistics is Goal difference, obviously a positive goal difference is better, but how would you determine a percentage value for that?
For example:
Team1 = +20
Team2 = -5

I was thinking if a team had a greater goal difference, then to just add a (say) 50% into the forumla to calculate their final overall percentage but that wouldn't be fair if it was only marginally different.


Advice is greatly appreciated