The problem is that linspace most likely is not creating a vector that only contains the user inputted values at the beginning and end. Let's say t=[2 3 4 5 ... 15]. If I inspect the interval around 3, I see that tn = [... 2.963 2.976 2.989 3.002 3.015 3.028 ...].
When creating indx1, the first segment with end at 2.989 but the second will start at 3.002. Visually, this will appear as a gap between these two points.
Your easiest solution is to create tn inside your for loop for each segment. That way, the end points always match the previous and next segments, and your "resolution" is less affected by the value of n.
