from bumps.names import *

def fn(x, a, b):
    return (a + b) * x


sigma = 1
x = np.linspace(-1.0, 1, 40)
dy = sigma * np.ones_like(x)
y = fn(x, 5, 5) + np.random.randn(*x.shape) * dy

M = Curve(fn, x, y, dy, a=(-20, 20), b=(-20, 20))

S = Parameter((-20,20), name="sum")
M.b = S-M.a

problem = FitProblem(M)