Getting different values on differentiating

Hey guys, here i am attaching two matlab files. I call practice4 in practice1. There is a problem by the way i am getting the values in the plot. In practice1, if i put t=1*5676.808 in the plot on abscissa [0,90,180,270,360] respective values on ordinate are [270,270.9,269.4,268.3,269.2].The issue comes when i change (t=2*5676.808 or t=3*5676.808) in the plot for abscissa [0,90,180,270,360] respective values on ordinate are [270,270.9,269.4,267.8,268.8]. If you can examine the very same values on ordinate has got changed for abscissa values of 270 & 360. I don't understand quite clearly why this happens. I expect all the values are same. Could you sort this out for me. Thanking you in advance.

[darova]

The question is too complicated. Please attach some pictures or something. Explain more, simplify the question

[satish kumar]

Hi darova, I am attching two of the figures down here. If you observe the figures you can understand what i am trying to explain on top. Thank you for the response.