Hi Damiano,
I understand that you would like to change the value of array passed to 'arrayfun'.
B = arrayfun(func,A1,...,An) applies func to the elements of the arrays A1,...,An, so that B(i) = func(A1(i),...,An(i))
Since arrayfun access is element wise 'z' passed to function is scalar and hence z(y) is not possible. The following code would help you to change the value of array passed directly
a={[3,7,9,5,11,2]};
b={[1,2,3,4,5,6]};
l={[1,0,0,0,0,0]};
f=@(x,z,y) x.*z(y);
l=cellfun(f,a,l,b,'UniformOutput',0);