Scratch

skippito · 2012-05-27 15:31:19

I need a script that calculates pi.

amcerbu · 2012-05-27 16:10:39

You should check out the Wikipedia page. There are many algorithms for calculating Pi. My favorite is this the Gauss-Legendre Algorithm. Here's how it works:


set Accuracy ▼
 to 50
 Choose a big number.
set a.n ▼
 to 1
set b.n ▼
 to 1
/sqrt ▼
 of 2
set t.n ▼
 to 0.25
set p.n ▼
 to 1
repeat Accuracy
set a.n+1 ▼
 to a.n
 + b.n
 / 2
set b.n+1 ▼
 to sqrt ▼
 of a.n
 * b.n
set t.n+1 ▼
 to t.n
 - p.n
 * a.n
 - a.n+1
 * a.n
 - a.n+1
set p.n+1 ▼
 to 2
 * p.n
set a.n ▼
 to a.n+1
set b.n ▼
 to b.n+1
set t.n ▼
 to t.n+1
set p.n ▼
 to p.n+1
set Pi ▼
 to a.n
 + b.n
 * a.n
 + b.n
 / 4
 * t.n

fuz50 · 2012-05-27 16:58:02

I'm not sure what you need it for, but if you don't need it this accurate, 355/113 is pretty darn close up to the 7th decimal place.

sanjayraj · 2012-05-27 17:32:57

You could do something like this:

when  clicked
delete all
 of pi
add thing
 to Pi
set PI
 to 0
set Fractions
 to 1
forever
set PI
 to PI
 + 4
 / Fractions
change Fractions
 by 2
set PI
 to PI
 - 4 / Fractions
change Fractions
 by 2
say Pi
replace item 1
 of Pi
 with PI

amcerbu · 2012-05-27 17:50:55

sanjayraj wrote:

You could do something like this:

when  clicked
delete all  ▼
 of Pi ▼
add thing
 to Pi ▼
set Pi ▼
 to 0
set Fractions ▼
 to 1
forever
set Pi ▼
 to Pi
 + 4
 / Fractions
change Fractions ▼
 by 2
set Pi ▼
 to Pi
 - 4
 / Fractions
change Fractions ▼
 by 2
say Pi
replace item 1
 of Pi ▼
 with Pi

Fixed your scripts.

Last edited by amcerbu (2012-05-27 23:06:31)

sanjayraj · 2012-05-27 19:04:53

Ok, thanks for fixing my scripts!

Splodgey · 2012-05-28 06:20:02

I have a Pi calculating project, if none of these work. The scripts there might help.

Last edited by Splodgey (2012-05-28 06:20:35)

skippito · 2012-05-28 14:25:39

amcerbu wrote:

You should check out the Wikipedia page. There are many algorithms for calculating Pi. My favorite is this the Gauss-Legendre Algorithm. Here's how it works:


set Accuracy ▼
 to 50
 Choose a big number.
set a.n ▼
 to 1
set b.n ▼
 to 1
/sqrt ▼
 of 2
set t.n ▼
 to 0.25
set p.n ▼
 to 1
repeat Accuracy
set a.n+1 ▼
 to a.n
 + b.n
 / 2
set b.n+1 ▼
 to sqrt ▼
 of a.n
 * b.n
set t.n+1 ▼
 to t.n
 - p.n
 * a.n
 - a.n+1
 * a.n
 - a.n+1
set p.n+1 ▼
 to 2
 * p.n
set a.n ▼
 to a.n+1
set b.n ▼
 to b.n+1
set t.n ▼
 to t.n+1
set p.n ▼
 to p.n+1
set Pi ▼
 to a.n
 + b.n
 * a.n
 + b.n
 / 4
 * t.n

Thanks! I used your script and it worked perfectly. You can find the final product here: http://scratch.mit.edu/projects/skippito/2569922

amcerbu · 2012-05-30 02:33:09

I'm glad it worked out for you! That particular pattern converges very quickly. Unfortunately, Scratch floating-point values have a small number of digits after the decimal...

likegames · 2012-05-30 18:58:19

Here is my (very slow) pi calculator:

when  clicked
delete all  ▼
 of pil ▼
add 4
 to pil ▼
set no ▼
 to 1
set pi ▼
 to 4
set +/- ▼
 to 0
forever
replace item 1  ▼
 of pil ▼
 with pi
if +/-
 = 0
change pi ▼
 by 4
 /no
*-1
set +/- ▼
 to 1
else
change pi ▼
 by 4
 /no
set +/- ▼
 to 0
change no ▼
 by 2

You can find the (very slow) calculator on my profile.
It uses the formula (4/1)-(4/3)+(4/5)-(4/7)+(4/9) and so on.

Last edited by likegames (2012-05-30 19:02:22)

Scratch

archived forums

#1 2012-05-27 15:31:19

Pi calculator

#2 2012-05-27 16:10:39

Re: Pi calculator

#3 2012-05-27 16:58:02

Re: Pi calculator

#4 2012-05-27 17:32:57

Re: Pi calculator

#5 2012-05-27 17:50:55

Re: Pi calculator

sanjayraj wrote:

#6 2012-05-27 19:04:53

Re: Pi calculator

#7 2012-05-28 06:20:02

Re: Pi calculator

#8 2012-05-28 14:25:39

Re: Pi calculator

amcerbu wrote:

#9 2012-05-30 02:33:09

Re: Pi calculator

#10 2012-05-30 18:58:19

Re: Pi calculator

Board footer