In each of your calls to plot(), you are plotting single values. The values plotted in one iteration won't connect to the values plotted in the previous iteration. This is fine for your blue plot, because you set the markers to points, which is why you can see the blue plot. The red plot, however, is not showing at all because you did not set the marker, instead you set the line style to solid. Note the difference between these two, where I'm plotting single values:
>> plot(1,1,'-') % line style set to solid
>> plot(1,1,'.') % marker set to point
You will be able to visualize both plots if you instead pass arrays into plot(). In each iteration, try plotting all values from 1 through k:
hplot = plot(plotX(1:k),hmid2(1:k),'.b',plotX(1:k),hamid2(1:k),'-r');
and taking out the hold on.
