> This is certainly ***NOT*** correct. (If you really got those numbers > from Matlab, then Matlab is up to Puttee.)
It was my mistake =) I had calculated the straight line so the edge of the plot was the y-axis =) > Have you plotted your data? > > (1) Fitting a straight line is ridiculous. Yes, I guess we have to realise that in the project, and explain why it is not good enough =) Next step is to use exponential smoothing =) > (2) If you are so foolish as to fit a straight line, you get > theta to have entries -4197.96 (intercept) and 2.16 (slope). > The line y = 79.69 + 0.18*x is off the edge of the graph and > does not even appear. It was clearly a bad mistake of mine! =( > Yes. The expression (t(x)%*%x)^(-1) is the matrix of entry > by entry reciprocals of the entries of t(x)%*%x. > > You want: > > theta <- solve(t(x)%*%x))%*%t(x)%*%y Thanks =) > Anyhow, if you're going to use R, why not ***use R***? > > fit <- lm(fpi ~ rtime,data=fuelData) > theta <- coef(fit) > > This gives an answer identical to that from the corrected version of > your ``from scratch'' expression. (That expression, while > theoretically > correct, is numerically ill-advised. The cognoscenti use either the > Choleski or the ``qr'' decomposition of t(x)%*%x to effect the > calculations. This is great stuff! ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
