Loops are not always necessarily slow. However, the vectorized code is much more cleaner and readable. For the simple example, you can use automatic array expansion introduced in some recent release of MATLAB. The following two code are equivalent.
a=[1;2;3;4;5]; b=[6;7;8;0;0];
z=zeros(5,5);
for i=1:5
z(: , i)=a(i)*exp(-b);
end
and
a=[1;2;3;4;5]; b=[6;7;8;0;0];
z = a.'.*exp(-b); % note a is used as a row vector and b is used as a column vector
