#!/usr/bin/ruby
func regress(x, y, degree) {
    var A = Matrix.build(x.len, degree+1, {|i,j|
        x[i]**j
    })
    var B = Matrix.column_vector(y...)
    ~((~A * A)**(-1) * ~A * B)
}
func poly(x) {
    3*x**2 + 2*x + 1
}
var coeff = regress(
    10.of { _ },
    10.of { poly(_) },
    2
)
assert_eq(coeff, [[1,2,3]])
say "** Test passed!"