It's not quite empty--it's just plotting a single point as a tiny dot. That's because you've only solved for a single point.
It looks like you're trying to do a five-point moving mean. You did the five-point mean part perfectly, but you forgot to move it! So try using a for loop to calculate the five-point moving mean for each point in the y vector. (You might need to skip the first and last few points because the moving window would need to start before the first index and end after the last index.)
Here's a start:
ym(k) = <the mean of a 5 point window>;