'Index/slice into the expression.
Parameters
arg_objs : list
LinExpr for each argument.
size : tuple
The size of the resulting expression.
data : tuple
A tuple of slices.
Returns
tuple
(LinOp, [constraints])'

@staticmethod
def graph_implementation(arg_objs, size, data=None):

    obj = lu.index(arg_objs[0], size, data[0])
    return (obj, [])
