why regstats give an error when I try to build a quadratic model

5 次查看（过去 30 天）
Vincent Moron
Vincent Moron 2013-1-11
Hello
I am trying a very simple model for a parabola with noise
>> Y=sin([0:0.01:pi])+rand(1,315)/1; >> X=[1:315]+rand(1,315); >> % X is my data and Y is considered to be the response >> regstats(Y,X,'quadratic')
returns
Warning: The exact method is impossible. Will be forced to use approximate method. > In stats/private/pvaluedw at 46 In dwtest at 74 In regstats at 352 In regstats at 155
If I inverse
>> s=regstats(X,Y,'quadratic')
>> s.rsquare
ans =
1.3575e-04
it works but then the rsquare is close to zero while it is a simple parabola and the model should be efficient. I expect a rsquare close to 1 ?
Any help for the two different issues is welcome
Vincent
Thanks in advance
Vincent

请先登录，再回答此问题。

采纳的回答

Tom Lane
Tom Lane 2013-1-11
编辑：Tom Lane 2013-1-11
The warning is just an indication that the significance of the Durbin-Watson statistic is outside the range of a table of exact values, so the quantity is being approximated. That should not be a problem for you.
When I try your example I get rsquare around 0.5 each time. If you plot X vs. Y you will see there is substantial scatter, so I would not expect a value near 1. I can't reproduce your result showing a value near 0.

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Model Building and Assessment 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by