The portion after the function name can only be parameter names, not expressions. You appear to be using parameters depth, neighboure_Noise, and p, so you would need something like
function y = f_function(depth, neighboure_Noise, p)
y=(1/rand(1,1)*depth*neighboure_Noise(p));
end
You would not be able to run that by click the green arrow: you would have to go down to the command line and pass in appropriate parameters, such as
Noise = sort(rand(1,50));
noise_index = 17;
depth = 14.38;
result = f_function(depth, Noise, noise_index)
