Dear All, Thank you for your replies. That will definitly get me started.
Ted: I said optimize because I suppose that an exact solution does not necessarily exists sometimes. Best, Emmanuel On 4/5/07, Ted Harding <[EMAIL PROTECTED]> wrote: > On 05-Apr-07 13:05:29, Emmanuel Levy wrote: > > Dear all, > > > > Could you please point me out to a function or set of functions > > that would allow me to optimize positions on the 2D map of points > > for which I are distance contrainted? > > > > for example, if I have: > > a b c > > a 0.0 0.5 0.7 > > b 0.5 0.0 0.3 > > c 0.7 0.3 0.0 > > > > I would like to obtain (x,y) coordinates to plot A,B,C so that the > > distance constraints are satisfied. i.e. a is 0.5 far from b, and o.7 > > far from c. etc ... > > > > Many thanks for your help, > > > > Best, > > > > Emmanuel > > Probably any of the multidimensional scaling functions variously > available would do (it is not clear what you mean by "optimize", > though). In your example above, an exact solution exists. > > For example > > library(MASS) > D<-matrix(c(0.0, 0.5, 0.7, 0.5, 0.0, 0.3, 0.7, 0.3, 0.0),nrow=3) > rownames(D)<-c("a","b","c") > colnames(D)<-c("a","b","c") > > P<-isoMDS(D)$points > plot(P[,1],P[,2],pch="+",col="blue") > > P > ## [,1] [,2] > ## a 0.39114338 0.03809598 > ## b -0.08358748 -0.11884547 > ## c -0.30755590 0.08074949 > > dist(P) > ## a b > ## b 0.5 > ## c 0.7 0.3 > > The last result shows that the distances betweem the three points > in the 3 rows of P are as desired: a<->b=0.5, a<->c=0.7, b<->c=0.3 > > Hoping this helps! > Ted. > > -------------------------------------------------------------------- > E-Mail: (Ted Harding) <[EMAIL PROTECTED]> > Fax-to-email: +44 (0)870 094 0861 > Date: 05-Apr-07 Time: 16:29:49 > ------------------------------ XFMail ------------------------------ > ______________________________________________ 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.