On Wed, Oct 21, 2009 at 12:09 PM, FMH <kagba2...@yahoo.com> wrote: > Dear All, > > Let have 10 pair of observations, as shown below. > > ###################### > x <- 1:10 > y <- c(1,3,2,4,5,10,13,15,19,22) > plot(x,y) > ###################### > > > Two fitted models, with ranges of [1,5] and [5,10], can be easily fitted > separately by lm function as shown below: > > ####################### > mod1 <- lm(y[1:5] ~ x[1:5]) > mod2 <- lm(y[5:10] ~ x[5:10]) > ####################### > > I'm looking for the interception points between these two straight lines from > these fitted models, mod1 and mod2. > > Could someone advice me the way to do it? > > Thank you > Fir
extract the coefficients, rearrange in a linear system, use solve. > > m1 <- as.matrix(rbind(coef(mod1), coef(mod2))) > a <- cbind(c(1,1), -m1[, 2]) > a [,1] [,2] [1,] 1 -0.900000 [2,] 1 -3.257143 > b <- m1[,1] > solve(a=a,b=b) [1] 4.396364 4.551515 This seems to "visually verify" the result: > plot(1:10,1:10, type="n") > abline(mod1) > abline(mod2) -- Paul E. Johnson Professor, Political Science 1541 Lilac Lane, Room 504 University of Kansas ______________________________________________ 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.