def lstsq(a, b, rcond=-1):
if rcond != -1:
raise Exception('non-default rcond not yet implemented')
x = Ch(lambda a, b : pinv(a).dot(b))
x.a = a
x.b = b
residuals = ch.sum( (x.a.dot(x) - x.b) **2 , axis=0)
rank = NotImplementedError
s = NotImplementedError
return x, residuals, rank, s
