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-   Chapter 3 - The Linear Model (http://book.caltech.edu/bookforum/forumdisplay.php?f=110)
-   -   Assumption in Problem 3.9 (http://book.caltech.edu/bookforum/showthread.php?t=4876)

Fromdusktilldawn 01-22-2019 11:01 PM

Assumption in Problem 3.9
 
In Problem 3.9, it stated that X^TX is positive definite

Which means it is also invertible

But on page 85, it said that X^TX might not be invertible.

Can someone explain this disparity?

htlin 01-23-2019 03:02 AM

Re: Assumption in Problem 3.9
 
Problem 3.9 asks you to solve a special case (invertible case) of the more general task (on page 85).

Hope this helps.


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