# Happy Birthday, Nobilis and hiimhere

Submitted by Zandu Ink on Mon, 11/23/2009 - 7:25am

Yet another couple of birthdays today!

Here's to aging like a fine wine and here's to... being old enough to smoke in Alabama. (I know it's a stretch. So sue me. (Don't really. I'm looking at you, LawyerBoy.))

Man, with all these birthday wishes, I feel like Frosty the Snowman.

Forums:

TheBoy

Mon, 11/23/2009 - 7:30am

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## happy birthday both of you.

happy birthday both of you. here's to one last year of teenage drama (it won't necessarily go away, it just won't be teenage anymore.)

Amiable Hummingbird

Mon, 11/23/2009 - 9:47am

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## Well my goodness!

We seem to be having a flood of birthdays lately!

So Happy Birthday to you both - I hope the two of you are having fantastic days, and even better nights!

Gudy

Mon, 11/23/2009 - 12:19pm

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## Well, with almost 500...

... registered users, it stands to reason that the probability of there being a birthday every day is getting comfortably close to unity.

Also, Happy Birthday to you guys!

TheBoy

Mon, 11/23/2009 - 12:37pm

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## no way. step 1: if there are

no way.

step 1: if there are 23 people, it's better than 50-50 that there's a shared birthday.

(TB consults TBB (that's TB's Brother), a mathy type)

TBB's guess for 500 people is 272 birthdays represented, assuming uniform distribution of birthdays and no Feb. 29 birthdays.

a little google reveals:

(that is to say: the odds of all birthdays represented among (People))--2000 people, 21% chance. 500 people: almost no chance atawl.

P(500)=9.8...*10^(-70)

P(1000)=1.7...*10^(-17)

P(1500)=0.001978...

P(2000)=0.2161...

P(2500)=0.6804...

P(3000)=0.9072...

P(4000)=0.9756...

P(4500)= 0.9984...

P(5000)=0.99959...

P(10000)=0.999999999555....

from http://www.physicsforums.com/archive/index.php/t-129658.html

Amiable Hummingbird

Mon, 11/23/2009 - 2:07pm

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## jeeeez

Trying to follow that gave me a headache. Way too many numbers for my liking.

TheBoy

Mon, 11/23/2009 - 2:19pm

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## A little more simply: For all

A little more simply: For all birthdays to be represented, 500 people is highly unlikely.

REALLY highly unlikely.

2000 people, about 21%

2500 people, a little more than 60%.

V

Mon, 11/23/2009 - 5:03pm

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## Screw analytics

Screw analytics, we have computers!

A reasonably precise answer will be fine. While it will be hard to hit *every* birthday, it will be easy to hit *most* birthdays, thus assuring that almost every day will have a birthday.

nPeople = 100;

nTests = 10000;

birthdays = zeros(nTests,1);

for iT = 1:nTests;

birthdays = round(365*rand(nPeople,1));

nBirthdays(iT) = length(unique(birthdays));

end

mean(nBirthdays)

ans = 87.6094

In english: With 100 people, distributing the birthdays randomly they will cover an average of 87.6 different days after testing 10,000 times. This ignores leap year birthdays, which would reduce it a smidge. I guess you could do rand(1461) and divide the mean by 4 if you wanted better accuracy.

But anyway:

test(100) = 87.6 different birthdays, on average, for 100 people

test(200) = 154 different birthdays, on average, for 200 people

test(300) = 205

test(400) = 243

test(500) = 273. With 500 people entering birthdays we have 273/365 or a 75% chance that tomorrow will have at least one birthday. We have those same odds every day (ignoring seasonal variations, if any). Gudy is correct if ".75" is reasonably close to "1"

test(1000) = 342, or a 94% chance that every birthday is represented.

Gudy

Tue, 11/24/2009 - 12:49am

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## That's what I was...

... getting at, yes, poorly worded though my original claim might have been. Screw hitting every day. If we have a good chance of having a birthday thread three days out of four, that's close enough to having one every day for it to be no longer that remarkable.

Marri

Tue, 11/24/2009 - 3:37pm

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## What language is that?

It's either one I don't recognize or simplified for non techies. Or both

V

Tue, 11/24/2009 - 5:44pm

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## MatLab

And both It's optimized for people in signal processing, image analysis, or others who work with large volumes of data and throw a little of this and a little of that at them...good for rapid prototyping, not so good for compiling and deploying. But the support for matrix operations is phenomenal I wrote the code as executed, tho (well...almost. I actually drafted it up on a single line since I was too lazy to make a script file).

Marri

Tue, 11/24/2009 - 8:50pm

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## Oh lord

We use MatLab in our Computational Mathematics for Engineers program, and I'm taking my first CME class this winter. And it's 102, and everyone else will have taken 100, and I will be behind everyone in MatLab and it will be deathly!

...except that I'm CS. So I already know how to code. But I'm stressing about it anyway?

V

Tue, 11/24/2009 - 10:29pm

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## Oh man, don't worry

If you can program *anything* else including BASIC, you can pick up MatLab with little or no trouble. The biggest problem will be not realizing MatLab already has a built-in function for (whatever), has probably already optimized it, but is hiding it under some name that wasn't obvious to you. Having a friend who's fluent or learning to use the help to find functions is a big plus. You'll be coding circles around people who are still trying to figure out what a "for" loop is.

MeiLin

Mon, 11/23/2009 - 1:57pm

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## happy birthday, Nobilis and hiimhere!

My favorite erotic podcaster, and a lurker! delurk! delurk!

Nobilis

Mon, 11/23/2009 - 9:13pm

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## I'm here!

I'm here! I'm here!

Delurking on the last hour of my birthday, because you asked so nice.

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