Matrix multiplications
Dear R users: I have written the following lines :
x=c(10,11,12,13,14,17,15,16,10,11,41,25,26,14,12,14,15,20,14,22) x=matrix(x,ncol=2) a=matrix(1,nrow(x),1) X=cbind(a,x) y=c(12.00, 11.00, 13.00, 12.50, 14.00, 18.50, 15.00, 12.50, 13.75, 15.00)
b=solve(t(X)%*% X)%*% t(X)%*% y
when I wrote the following line
(t(y-X %*% b)%*%(y-X %*% b)/(length(y)-ncol(X)))*solve(t(X)%*% X)
I have obtained an error message, I don't know why namely (t(y-X %*% b)%*%(y-X %*% b)/(length(y)-ncol(X))) is a scalar:
(t(y-X %*% b)%*%(y-X %*% b)/(length(y)-ncol(X)))
[,1] [1,] 3.620354 Can you please help me. Thank you George