in your for loop is an end missing. I guess that this missing end should be positioned before your plot commands.
Then the following line throws an error:
I think it should be:
dis(i+1) = delF(i+1)/Keff;
After fixing this there are some errors appearing due to different lenghts of x- and y-values whole plot is running, which is a result from your for loop and should be solved by you. Note that sbx has a length of 20001.
If you solved this then your plots will overwrite eachother, so a recommendation would be to use subplot to show all results in one figure.
I hope this helped, if not come back with more questions.