Hey gang!
This is my first post to the list, but I will try to be as precise as possible.
I have googled around and can't find an easy explanation for why this is
happening, so I figured I had better get some help from the experts, so thanks
in advance! My code is supplied below. I am running R 2.15.1 on Mountain
Lion, 64-bit. OSX is 10.8.2
I want to plot iso-efficiency lines for a hypothetical device. I have a
fully-parameterized expression, and have checked its sanity by hand, and it
appears to operate as it ought to. However, when I use the contour() function,
the contour lines it produces don't lie in the correct place. I generally
believe their shape, but they appear to be translated by some amount. I know
that the analytical expression produces a given value, but when I look for that
point on the plot, the iso-efficiency line doesn't cut through the point. This
is illustrated in the following code by the blue circle. That point should
fall on the red line, but clearly it does not. Nevertheless, the governing
equation (as defined in the R code) produces the correct result (if you check
the array "Electrolyzer", the numbers match what you would get from simply
applying the appropriate values to the expression, so it isn't a problem in the
iterative population of the array). I tried varying the mesh !
size (i.e. the number of points in the vectors etaELEC and FE), but of course
this didn't have any effect besides smoothing the curves out a bit more. I
also thought that it might be a problem with the png output, but I tried
generating the figure in the quartz window, and the error persists. I also
tried closing R, not saving the workspace, reopening, making a completely new
working directory, and then re-entering the functions. In all cases, the plot
still ends up funky.
Is there something fundamental that I am missing about the contour plot
function? Also, for those playing along at home, the code includes an "easy"
way to add subscripts after special characters in a plot title (which is
typically a useful feature). Relevant code is pasted below:
Ecap <- function(etaELEC,FE,etaFC,etaRP,ENH3,etaCOMP,etaST)
{(etaELEC)/((1+((1-FE)/(FE*1.43))*(1-etaST*etaELEC+((1.2*1.43*etaELEC)/(etaRP*ENH3)))+((7.3*etaELEC)/(2*etaCOMP*ENH3))+((25*etaELEC)/(etaRP*ENH3))))}
etaELEC <- seq(from=0.05,to=1, by=0.01)
FE <- seq(from=0.05,to=1, by=0.01)
Electrolyzer <- array(0,dim=c(length(etaELEC),length(FE)))
for (i in 1:length(etaELEC)){
for (j in 1:length(FE)){
Electrolyzer[i,j]<-Ecap(FE=FE[j],etaST=0,etaFC=0,etaELEC=etaELEC[i],etaRP=0.6,etaCOMP=0.95,ENH3=340)}}
png(file="Standalone.png",bg="transparent",height=5400,width=5400,res=864)
par(family="serif",tck=0.01)
plot(0, type="n", xlim=c(0,1),ylim=c(0,1), cex.lab=1.2, main="Energy Capture
Coefficient for Standalone Device", xlab="Electrolyzer Voltage Efficiency",
ylab="Faradaic Efficiency", cex.sub=0.75, sub=expression(paste(eta,""[FC],"=0,
",eta,""[Comp],"=0.95, ",eta,""[Sterling],"=0, ",eta,""[RP],"=0.60, "))) #make
blank plot box with correct axes, etc...
contour(x=seq(0,1,length.out=(nrow(Electrolyzer))),y=seq(0,1,length.out=(ncol(Electrolyzer))),Electrolyzer,axes=FALSE,levels=c(-0.1,0,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1))
contour(x=seq(0,1,length.out=(nrow(Electrolyzer))),y=seq(0,1,length.out=(ncol(Electrolyzer))),Electrolyzer,axes=FALSE,levels=c(0.102),col="red")
points(0.5,0.1547,col="blue")
dev.off()
________________________
Thomas Veltman
Kanan Lab
Department of Chemistry
Stanford University
[email protected]
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