Does the number of parameters available in an equation equals to the number of parameters to be optimized in the Genetic Algorithm?

I stumbled upon a journal which the author is activating genetic algorithm together with Simulink model via M function.The Simulink model applied is a SISO system and therefore the M function (to activate genetic algorithm) only accept 1 input at one time.The fitness function to be optimized is integral of the time absolute error (ITAE). The author is using genetic algorithm to optimize a PID controller which contains THREE PARAMETERS.

If I am not mistaken, in genetic algorithm the number of output will be equal to the number of input substituted into the genetic algorithm.I am confuse here....Can someone kindly guide me on this.Thanks.