/usr/share/doc/ruby-gsl/examples/integration/ahmed.rb is in ruby-gsl 2.1.0.3+dfsg1-1build1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | #!/usr/bin/env ruby
# Ahmed's Integral
# See e.g. http://mathworld.wolfram.com/AhmedsIntegral.html
#
require("gsl")
include GSL
include Math
f = Function.alloc { |x|
sqrtx22 = sqrt(x*x + 2)
atan(sqrtx22)/(sqrtx22*(x*x + 1))
}
val = f.qng(0, 1)[0]
puts("Ahmed's integral")
puts("Expect: 5pi^2/96 = #{5.0*M_PI*M_PI/96}")
puts("QNG result: #{val}")
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