March 14th - Happy Pi Day everyone!!

It’s my wedding anniversary, too. Only thirty here, though. So, belatedly, happy pi day, happy Einstein’s birthday, and happy anniversary to you and your lovely wife.

Circle, I’ve got your number
digits so sweet and fine
circumf’rence over diameter
three point one four one five niiiine
three point one four one five niiiine

I think you can guess the tune. :slight_smile:

RTFirefly I’m not sure if I want to have your babies for that, or kill you for the mindworm.

Well done :slight_smile:

Damn you, Firefly! Now I’m off to YouTube to listen to “Jenny”!

My Facebook status on March 14 (and still is, as I rarely change it) was:

I’ll leave it without comment, as I know Dopers are smart enough to see what I just did there.

Please, do tell how do you hand calculate pi? Is it by an infinite series of fractions?

My daughter is a pi baby. I was actually a little dissapointed when 1:59 AM passed, since I knew she wouldn’t make it to 1:59PM. And 3.14.5:34 doesn’t mean a whole lot.
Yes, she did get pie instead of cake for when she turned two last week!

Some friends had their daughter at exactly 1:59 AM on Monday morning. Now they’re worried she might grow up to be a mathematician. :wink:

HURRAY!!! A geek question for me :smiley:

Pi= circumference / diameter. It doesn’t matter how large the circle is, the math works out the same always.

I’ve never used fractions for Pi, its always been long division. Plug in the numbers and start subtracting.

I’m kinda new…was this my first woosh? If not, I’d be thrilled to talk Pi with you…cause I don’t understand how one would use fractions for Pi.

I’m afraid that it might be even worse than that. She might grow up to be an engineer :eek:

Next year, you are invited to the Community College where I work. A week before pi day we set up a jar for each science professor. Students, staff and faculty put money in the jar of the professor that they wanted to see get a pie in the face. Some shenanigans similar to episodes of ‘Survivor’ transpired (long story), but in the end, our psychology professor was pi-ed. Good times!

Well, Pi Day has come and gone. It was fun while it lasted, but now it is time to look forward to… Tau Day! While it does not have the same cool, hipster aura to it, it is clearly a superior day. In fact, one could even say it is perfect. To Tau Day!

I know, but you need accurate values for circumference and diameter. Do you just draw a large circle and measure them?

I did a maths class that mentioned a few ways to calculate pi. Looking at the Wikipedia page, there are several infinite series for pi, which you could use to calculate it by hand. The difficult part is when you get to smaller and smaller decimal places, which is why I was wondering how you could calculate it to 6 pages.

Oh, there are more formulae at Pi Formulas -- from Wolfram MathWorld

I think that we need to keep this thread open…because you are trying to learn how irrational us geeks can be.

PS… Pi is an irrational number

Well, as someone noted earlier, for those of us whose dates aren’t backward, Pi Day should actually be 31 April – which maps conveniently to 1 May, which is May Day, so a twofer! Which makes Tau Day 62 August, or 1 October. Easily remembered!

Or maybe they should just be 3 January and 6 Feburary, if you’re not into too many decimal places.

Er, if you’re just measuring, you won’t be able to get pi, unless you have infinite accuracy. Why? Irrational numbers can’t be expressed as fractions. When you divide circumference by diameter, that’s actually a fraction. Another thing: all fractions end up as decimals with repeated sequences, so you can’t keep dividing for long :smiley:

If the circumference or diameter itself is irrational, dividing the circumference by the diameter would give you an irrational number. But you’re not going to be able to take a physical, real-world measurement and get an irrational number.
I find it interesting that, even though pi has been known as a special number for thousands of years, it’s only since the 1700’s that it’s been called “pi” (i.e. that the symbol π has been used). And it was only proved to be irrational in 1761. (By contrast, the ancient Greeks knew that the square root of 2 is irrational.)

You are right, of course. You can’t get good numbers with a stew can and a ruler. I usually go wrong 4 or 5 digits into the call. When I check my numbers with a calculator, my results are correct according to the data. GIGO happens:)

I’ve never been good with fractions, so the first thing I do when dealing with them is convert them to decimals. I’m quite sure most of the Garbage In starts there.

I’m not trying to win a Nobel prize with my scribblings, its a something to do while ignoring the hold muzak. Some people draw flowers or fill in the letters. I do long division with paper and a number 2 pencil :smiley:

I only have π memorized out to the “2643” myself. Used to know it a little further.

AaronX - the limit of a series of rationals can be irrational. For instance, successive Fibonacci numbers have a ratio that converges to (1 + sqrt(5) ) / 2, a.k.a. φ, the so-called “golden ratio.”

flatlined - I think the question’s still sort of hanging as to what exactly it is you’re dividing by what (using long division of decimals or fractions, either way) to calculate π. Are you actually drawing a big circle and dividing circumference by diameter? (If so, the two follow-up questions: are you using standard 8.5 x 11" or A4, and how are you measuring the circumference? I think that’s why some readers here might be a bit perplexed.)

I actually spent some time a few weeks ago using the Pythagorean Theorem to work out how to approximate pi as a succession of perimeters of inscribed polygons in the unit circle, doubling the number of sides each time. Turns out that, as in iterative formula, it actually works out pretty nicely. Wouldn’t really work as flatlined’s method, because it involves taking square roots, but if you have a calculator it converges pretty quickly:

Let x_1 = sqrt(2) (the length of one side of the inscribed square). As a first approximation, π = 2x_1 ≈2.8284.

Then, iterate, starting with i = 2:
x_i = sqrt( 1 + 0.5x_(i-1) ) - sqrt( 1 - 0.5x_(i-1) ) ; π ≈ (2^i)x_i

You get:

x_1 ≈ 1.414213562 π ≈ 2x_1 ≈ 2.828427125
x_2 ≈ .7653668647 π ≈ 4x_2 ≈ 3.061467459
x_3 ≈ 0.3901806440 π ≈ 8x_3 ≈ 3.121445152
x_4 ≈ 0.1960342807 π ≈ 16x_4 ≈ 3.136548491

By the time you get to i = 10, your π value is accurate to the 5th decimal place. At that point the inscribed polygon has 2048 sides, each of length x_10 ≈ 0.003. You wind up gaining about one more digit of accuracy every two steps, until eventually your calculator’s precision limits start introducing rounding errors.

In other words, flatlined, you’re not the only one around here who does math when he’s bored. I’ve been experimenting with the arithmetic of continued fractions lately, myself.

And they say women are irrational (snicker!)