51 lines
1001 B
Ruby
51 lines
1001 B
Ruby
#!/usr/local/bin/ruby
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#
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# pi.rb
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#
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require "bigdecimal"
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#
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# Calculates 3.1415.... (the number of times that a circle's diameter
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# will fit around the circle) using J. Machin's formula.
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#
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def big_pi(sig) # sig: Number of significant figures
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exp = -sig
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pi = BigDecimal::new("0")
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two = BigDecimal::new("2")
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m25 = BigDecimal::new("-0.04")
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m57121 = BigDecimal::new("-57121")
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u = BigDecimal::new("1")
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k = BigDecimal::new("1")
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w = BigDecimal::new("1")
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t = BigDecimal::new("-80")
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while (u.exponent >= exp)
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t = t*m25
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u,r = t.div(k,sig)
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pi = pi + u
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k = k+two
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end
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u = BigDecimal::new("1")
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k = BigDecimal::new("1")
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w = BigDecimal::new("1")
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t = BigDecimal::new("956")
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while (u.exponent >= exp )
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t,r = t.div(m57121,sig)
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u,r = t.div(k,sig)
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pi = pi + u
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k = k+two
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end
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pi
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end
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if $0 == __FILE__
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if ARGV.size == 1
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print "PI("+ARGV[0]+"):\n"
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p big_pi(ARGV[0].to_i)
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else
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print "TRY: ruby pi.rb 1000 \n"
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end
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end
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