how to Implement a Fitness Function for comparison in genetic algorithm for matlab

Hi , Please can anyone give hints on syntax that can implement this fitness function for genetic algorithm matlab to compare measured and simulated results and also calculate the Root Mean Square Error. The simulation is a simple expression with the best values of the 5 input parameters to be extracted. Fitness function =∑((A(m)-A(p))^2 Root Mean Square Error = RMSE=Sqrt(∑(A(m)-A(p))^2/n)