probably a stupid question: MatLab equivalent of "diff" ?

[Stef Mientki]

Does anyone know the equivalent of the MatLab "diff" function.
The "diff" functions calculates the difference between 2 succeeding 
elements of an array.
I need to detect (fast) the falling edge of a binary signal.

There's derivate function in Python diff,
but when you use an binary (true/false) input,
it also detects rising edges.

Probably a stupid question,
but I still have troubles,
digging to huge amount of information about Python.

thanks,
Stef Mientki