Removed useless integration -- added derivative
Removed useless integration -- added derivative

palful/yambopy,palful/yambopy,alexmoratalla/yambo-py,alexmoratalla/yambopy,alexandremorlet/yambopy,alexandremorlet/yambopy,henriquemiranda/yambopy,henriquemiranda/yambo-py,alexmoratalla/yambo-py,henriquemiranda/yambopy,alexmoratalla/yambopy,henriquemiranda/yambo-py