# 李哲源

 Jul 11 comment Compute projection / hat matrix via QR factorization, SVD (and Cholesky factorization?)@bikeclub Hi friends, it has been nearly 3 years since I posted my answer and it appears to be well-received. Are you interested in accepting my answer? Thanks a million! Jul 9 awarded Nice Answer Jun 18 awarded Lifejacket May 22 awarded Enlightened May 21 awarded Good Answer May 20 comment Get hat matrix from QR decomposition for weighted least square regression@TomWenseleers The answer code is `n - 2 * sum(Q1 * Q2) + sum(crossprod(Q1) * crossprod(Q2))`, where `Q1` and `Q2` are as defined in the answer. `n = 50` in this answer’s example. I have verified that the computation result is correct compared with that of brutal-force computation. May 20 reviewed Edit VBA how to improve this code and make it more efficient? May 20 revised VBA how to improve this code and make it more efficient?added 4 characters in body May 20 reviewed Edit How can i perform search from all website pages? May 20 revised How can i perform search from all website pages?deleted 6 characters in body; edited body May 20 reviewed Edit How to use TypeConverters for calendar? May 20 revised How to use TypeConverters for calendar?added 22 characters in body May 12 awarded Yearling May 12 awarded Yearling May 5 answered why outputs of linear model from these 2 ways are different in R? May 3 reviewed Edit Auto Completion problem in Android Studio giving error May 3 revised Auto Completion problem in Android Studio giving erroradded 3 characters in body May 3 comment How to fit a line with fixed points? (in R)@Dianafreedom Use the `xout` argument in `approx` or `spline` for prediction at new locations. May 3 revised How to fit a line with fixed points? (in R)fix format of quotes May 2 answered How to fit a line with fixed points? (in R)