Code used to benchmark solutions in http://stackoverflow.com/questions/18201729/forcing-the-columns-of-a-matrix-within-different-limits

18201729.m

L = randn(20,3);
l1_max=20; l1_min=0.5;
l2_max=20; l2_min=0.5;
mu_max=20; mu_min=0.5;

tic
for kk=1:1e5
    l=L;
    for k=1:20
        if l(k,1)>l1_max
            l(k,1) = l1_max;
        elseif l(k,1)<l1_min
            l(k,1) = l1_min;
        end
        
        if l(k,2)>l2_max
            l(k,2) = l2_max;
        elseif l(k,2)<l2_min
            l(k,2) = l2_min;
        end
        
        if l(k,3)>mu_max
            l(k,3) = mu_max;
        elseif l(k,3)<mu_min
            l(k,3) = mu_min;
        end
    end
end
toc

tic
for kk=1:1e5
    l=L;
    l(l(:, 1) > l1_max, 1) = l1_max;
    l(l(:, 1) < l1_min, 1) = l1_min;
    l(l(:, 2) > l2_max, 2) = l2_max;
    l(l(:, 2) < l2_min, 2) = l2_min;
    l(l(:, 3) > mu_max, 3) = mu_max;
    l(l(:, 3) < mu_min, 3) = mu_min;
end
toc

This returns:

Elapsed time is 0.134269 seconds.
Elapsed time is 0.672458 seconds.