# metRology package

2 messages
Open this post in threaded view
|
Report Content as Inappropriate

## metRology package

 I'm having trouble with a simple application with metRology. I need to estimate the uncertainty of the density thickness of seven sheets of film. This is calculated from measurements of mass, length and width of rectangular samples of film. It's not too hard to calculate the whole thing with a little Monte Carlo loop. I get about 0.07 with this:         #sample area         L<-5*2.54 #cm         W<-8*2.54 #cm         #sample mass         m<-0.2543*1000 #mg         #uncertainties         L.u<-(1/16)*2.54 #cm (nearest 16th inch)         W.u<-(1/16)*2.54 #cm         m.u<-0.006*1000 #mg scale calibration data         denth<-c(0,0,0)         singth<-c(0,0,0)         for(i in 1:1e5) {           #denth[i]<-7*dt+sum(rnorm(7,0,dt.u))           for(j in 1:7)  singth[j]<-(m+rnorm(1,0,m.u))/((L+rnorm(1,0,L.u))*(W+rnorm(1,0,W.u)))           denth[i]<-sum(singth)         }         sd(denth) #0.07279882 Now with the metRology package, I get a much higher number, which is actually the seven times the uncertainty of one layer:         require(metRology)         d.set<-list(mass=m,Length=L,Width=W)         d.set.u<-list(m.u,L.u,W.u)         dent<-expression(7*(mass/(Length*Width)))         uncert(obj=dent, x=d.set, u=d.set.u, method="GUM") I've tried other ways of defining the expression and every method option. I suspect the expression is the problem area, but if so, I really need to know how to get it right for harder problems. Thanks in advance for any suggestions. - Mark         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.