def booth(xy):
x, y = xy<EOL>r1 = x + <NUM_LIT:2>*y<EOL>r2 = y + <NUM_LIT:2>*x<EOL>return np.array([r1, r2])<EOL>
The Booth's function, as a set of residuals (cost = sum(residuals**2))

The standard Booth function is with data as [7, 5], and has a single
global minimum at (1,3). It is a coupled linear model, with the
parameter and data space both 2-dimensional.

Parameters
----------
    - xy : 2-element list-like
        The x,y parameters of the model.

Returns
-------
    2-element list-like
        The residuals of the model.