Make y1 an array
y1(j1) = ......
and then keep track of min MSE like you do for anything that you want to keep track of min or max:
best_j1 = 1
minMSE = inf;
for j1 = 1 : 10
MSE(j1) = .... % Do calculation. Make array in case we want to inspect
if MSE(j1) < minMSE
best_j1 = j1;
minMSE = MSE(j1);
end
end
Or find it after the loop, instead of keeping track inside the loop:
[sortedMSE indexes] = sort(MSE, 'descend');
minMSE = sortedMSE(1);
best_j1 = indexes(1);
