How to choose an analytical expression for the graphics?

Good afternoon.

I have such a problem: "There is an electrical circuit. There is an input signal in the form of a graph, it is necessary to make the output signal". If it is short.

I have a chart:

Examples of the source data in the form:

tначальная = -10 seconds tконечное = 10 seconds U = -50 TO

And I need to record the aforesaid schedule in the form of analytical expressions in the likeness (example!):


To be precise, I still need to write a function that initialisere array float according to the set schedule (in the form of analytical expressions).