Address what to do when input to Reciprocal is 0

Right now when the input to a reciprocal is 0 the program crashes. This can happen for some matrices with zeros for the LDLT matrix inverse and should be addressed.

added Operations SFG generators labels

Since it is floating-point, one can detect it and set the value to either float('nan') or float('inf'). Same should hold for division.

mentioned in merge request !487 (merged)

closed with merge request !487 (merged)