On Jul 6, 2011, at 23:50 , David Winsemius wrote: > > On Jul 6, 2011, at 4:43 PM, Data Analytics Corp. wrote: > >> Hi, >> >> Suppose I have two vectors, not necessarily the same length (in fact, they >> usually are different lengths): y.1 that has increasing values between 0 and >> 1; y.2 that has decreasing values between 1.0 and 0. You can picture these >> as being supply (= y.1) and demand (= y.2) curves from economics. I >> typically plot these vectors on the same graph against a common x variable, >> which happens to be price for what I do. The price variable runs from, say, >> $0 to $25. When I plot y.1 and y.2, I've been eye-balling a vertical line >> at a price point where y.1 intersects y.2. I'm now tired of eye-balling a >> line through the intersection -- takes too much time to get it right or just >> close enough. I can't figure out how to find the price value at which the >> two curves intersect. Going back to the economics interpretation, I want >> the price where supply equals demand. Any suggestions as to how I can find >> that price point in R? Any functions that help? > > ?approxfun # or.. > ?splinefun # should allow you to make two functions and then solve for the > X taht minimizes the difference. >
With linear interpolation, uniroot() on the difference between the two approxfun()s should get you there rather quickly. (Unless the curves are very smooth, I'd avoid splinefun because of the risk of introducing oscillations.) > -- > > David Winsemius, MD > West Hartford, CT > > ______________________________________________ > 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. -- Peter Dalgaard Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ 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.
