[EMAIL PROTECTED] wrote: > This is probably a blindingly obvious question:
Yes, it is. > Why does it matter in the uniroot function whether the f() values at > the end points that you supply are of the same sign? Plot some graphs. Think about the *name* of the function --- *uni*root. Does that ring any bells? And how do you know there *is* a root in the interval in question? Try your ``uniroot2'' on f(x) = 1+x^2 and the interval [-5,5]. To belabour the point --- if the f() values are of the same sign, then there are 0, or 2, or 4, or .... roots in the interval in question. The ***only chance*** you have of there being a unique root is if the f() values are of opposite sign. The algorithm used and the precision estimates returned presumably depend on the change of sign. You can get answers --- sometimes --- if the change of sign is not present, but the results could be seriously misleading. Without the opposite sign requirement the user will often wind up trying to do something impossible or getting results about which he/she is deluded. cheers, Rolf Turner [EMAIL PROTECTED] P. S. If the f() values are of the same sign, uniroot() DOES NOT give a warning! It gives an error. R. T. ______________________________________________ R-help@stat.math.ethz.ch 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.