class MoreMath::LinearRegression

def tvalue(alpha = 0.05)
  df = @image.size - 2
  return 0.0 if df <= 0
  sse_y = 0.0
  @domain.zip(@image) do |x, y|
    f_x = a * x + b
    sse_y += (y - f_x) ** 2
  end
  mean = @image.inject(0.0) { |s, y| s + y } / @image.size
  sse_x = @domain.inject(0.0) { |s, x| s + (x - mean) ** 2 }
  t = a / (Math.sqrt(sse_y / df) / Math.sqrt(sse_x))
  t.nan? ? 0.0 : t
end