2D interpolation with rb-gsl in ruby

2dinterp_gsl.rb

xarr = GSL::Vector.alloc([-2.0, -1.0, 0.0, 1.0, 2.0])
yarr = GSL::Vector.alloc([-2.0, -1.0, 0.0, 1.0, 2.0])
a = []
xarr.each do |x|
  yarr.each do |y|
    a << x*x - y*y
  end
end
puts a.inspect # this array has been put into the C program
zarr = GSL::Vector.alloc(a)

i2d = GSL::Spline2d.alloc(GSL::Interp2d::BICUBIC, xarr, yarr, zarr)

xval = [1.0, 1.5, 2.0]
yval = [1.0, 1.5, 2.0]

puts i2d.eval(-1.5, 1.0)
puts i2d.eval(1.0, -1.5)

# OUTPUT
# -1.5 and 1.0 : -1.3392857142857142
# 1.0 and -1.5 : 1.3392857142857142