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Old 01-22-2019, 11:01 PM
Fromdusktilldawn Fromdusktilldawn is offline
Junior Member
Join Date: Sep 2017
Posts: 5
Default 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?
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