If you call a Simulink® function from multiple sites in a chart, all call sites share the state of the function variables. For example, suppose you have a chart with two calls to the same Simulink function at each time step.
The function f contains a block diagram that increments a counter by 1 each time the function executes.
At each time step, the function f is called twice, which causes the counter to increment by 2. Because all call sites share the value of this counter, the data y and y1 increment by 2 at each time step.
Note: This behavior also applies to external function-call subsystems in a Simulink model. For more information, see Create a Function-Call Subsystem in the Simulink documentation.