Math Time!

Ruby
1

Alright everybody! Math time!

So today I tried to write a program which would print out, say, 1000
digits of pi. I figured I’d do this by assigning a… variable…
to be a bignum… crap, Ruby is duck typing! I mean, yay?

Ok, so to the point. How do I tell Ruby to print a value (.to_f) to a
certain number of integers? .to_f(1000)? And also, how do I write
tan, cos, sin, etc. in Ruby?

Thanks for the help,
math rulez
--------------------------------------------|
If you’re not living on the edge,
then you’re just wasting space.

2

On 5/1/07, Ari B. [email protected] wrote:

Alright everybody! Math time!

So today I tried to write a program which would print out, say, 1000
digits of pi. I figured I’d do this by assigning a… variable…
to be a bignum… crap, Ruby is duck typing! I mean, yay?

Ok, so to the point. How do I tell Ruby to print a value (.to_f) to a
certain number of integers? .to_f(1000)? And also, how do I write
tan, cos, sin, etc. in Ruby?

I havent done this with numbers but you could use:

number.to_s[0…1000]

If u can do that without the convertion it should be better, but if
not i hope my solution helps you.

About maths check the Ruby builins Math module:

http://www.rubycentral.com/book/ref_m_math.html

3

On May 1, 2007, at 7:22 PM, Ari B. wrote:

So today I tried to write a program which would print out, say,
1000 digits of pi.

ruby -rbigdecimal -rbigdecimal/math -e ‘include BigMath; digits =
1000; puts “3.”+BigDecimal.PI(digits).to_s[3,digits]’

Ok, so to the point. How do I tell Ruby to print a value (.to_f) to
a certain number of integers?

printf “%.20f”, flt

.to_f(1000)? And also, how do I write tan, cos, sin, etc. in Ruby?

Math.tan(num) # etc.

James Edward G. II

4

— Todd B. [email protected] wrote:

puts pi( 1000 )

Oops! I meant → puts pi( 1e1000 )

5

— James Edward G. II [email protected]
wrote:

James Edward G. II

Or you could do it the hard way (yes, reinventing the
wheel is one of my faults)

we’ll just assume all computed variables

are BigDecimals

def pi( precision )
(0…precision).inject(0) { |sum, i| i*=4; sum +
1.0/(i+1) - 1.0/(i+3) } * 4
end

puts pi( 1000 )

900 times the age of the universe

later on my slow system …

3.14159…

this series takes my system about 6 seconds

just to get to 3.14159 (precision = 1_000_000)

and goes up about a factor of 10 for each additional

digit

for 1000 digits, you would need a precision

value of 1 followed by 1000 0’s (1e1000)

cos() converges almost immediately

def fact( i )
return i == 0 ? 1 : fact( i - 1 ) * i
end

def cos( angle, precision )
(0…precision).inject(0) { |sum, i| i*=4; sum +
anglei/fact(i) - angle(i+2)/fact(i+2) }
end

puts cos( 1.0, 3 )

0.540302305868092

require ‘mathn’
puts Math::cos(1.0)

0.54030230586814