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Hello PTC fam,
I don't know where did I do wrong in this programe.
the question is
Determine least square method value of coefficients Ci( i=0,...,m) in polynomial form.
Calculate the approximation error where m=3
Please advice.
Regards,
Adlil
Solved! Go to Solution.
Did you mean to do this:
Then:
Finally:
But there are options for minerr. If you press the right-mouse button on it, you can select other minimisation strategies. The above was done using 'Linear' (The default). For non-linear: Levenberg-Marquardt you may get:
Success!
Luc
Your sheet does not explain well what you are trying to achieve. Apart from that:
1. The summation for Toc in above picture goes from i=0 to m, when m=3, that means you should get C as a vector of 4 elements. Your sheet shows you calculate a vector C consisting of only three elements. The input for that calculation (matrix A and vector B) do not seem to be related to alpha or T.
2. Instead of the solve block, you can use the lsolve function to determine C from A and B:
3. What is the vector K calculated for?
Success!
Luc
Did you mean to do this:
Then:
Finally:
But there are options for minerr. If you press the right-mouse button on it, you can select other minimisation strategies. The above was done using 'Linear' (The default). For non-linear: Levenberg-Marquardt you may get:
Success!
Luc
Thank you for the reply. Pardon I should reconfirm back with you before hit the "accept the solution" button. I would like to ask
1. Does Gauss method is that simple ? Mind to explain why Gauss method we need to list like this compare to my version.
2. What is Minerr function is ?
3. Why do you sort vector T and alpha ?
Sorry if my questions didn't look smart since I really want to understand this program and the task given. Thanks again waiting for your reply.
I've been playing with this. A direct least squares fit to this data with a third order polynomial isn't great. But a fourth order fit to the natural logs looks pretty good. (My apologies for diverting the discussion!) Sheet in Prime 4.0 Express.
Thanks for the reply, didn't expect you achieve that close in the graph. Sadly I don't have Prime 4.0 appreciate for the help.
Here is a screenshot of Freds work (I just omitted the grid which can be achieved much easier in real Mathcad)
You can also create his function using Mathcads built-in polyfit function.
Here a comparison of a rational fit (f1), a polynomial fit of fourth order (f2) and Freds approach (f3).
According to the sum of squared errors the polynomial fit (f2) would win, but I bet you don't like the curve in the range from 2 to 5. So I guess that Freds approach rules.
MC15 sheet attached
Sadly I don't have Prime 4.0 appreciate for the help.
Any version of Prime above 3 will read my file.