Help with basics and finite difference method

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Will
Will 2014-9-14
评论： Will 2014-9-15
I have to write a program using the finite-difference formula to calculate the approximate value for the derivative of a function. The test will be tan(x) for x=1, determining the error by comparing with sec^2(x). I have no idea where to begin.

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Image Analyst
Image Analyst 2014-9-14
How about a for loop and taking the delta Y over the delta X where the separation is decreasing until it gets really really small, then compare to sec^2(x) and see how the difference gets smaller and smaller as the separation gets smaller and smaller. That's the finite difference method.
http://www.mathworks.com/matlabcentral/answers/8626-how-do-i-get-help-on-homework-questions-on-matlab-answers
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Image Analyst
Image Analyst 2014-9-15
OK, great, glad I could help. Can you go ahead and mark the answer as Accepted then?
Will
Will 2014-9-15
I will, but I just talked to my instructor and he explained that though your method is valid, I must use the given formula. Could I just do the same things we talked about, only replace slope with
slope = (tan(x+h)-tan(x))/h
and do the error vs. h plot? I'm going to use loglog(h, error, -s), but this gives me a weird window... Please let me know if you can help with that as well, though I understand if you don't want to. Thanks for helping!

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