[R] curvedarrow (some graphics problem)

[casperyc]

Hi there,

This is now the code

%%%%%
library(grid)

vp <-  viewport(
x = unit(0, "npc"),
y = unit(0, "npc"),
just = c("left", "bottom"),
xscale = c(-1, 1) ,
yscale = c(-1, 1))

vp2 <-  viewport( # probably not needed but I had trouble placing the xaxis
x = unit(0,    "npc"),
y = unit(0.5,  "npc"),
just = c("left", "bottom"),
xscale = c(-1, 1) ,
yscale = c(-1, 1))


pushViewport(vp)
grid.xaxis(at=seq(-1, 1, by=0.2), label=FALSE,  vp=vp2)
grid.points(x=0.3, y=0.5, gp=gpar(col=NA), default.units = "npc",   
name="h1", vp=vp)
grid.points(x=0.7, y=0.5, gp=gpar(col=NA), default.units = "npc",   
name="h2", vp=vp)
grid.text("s", x=0.3, y=unit(-1, "lines"), vp=vp2)
grid.text("t", 0.7, unit(-1, "lines"), gp=gpar(col="red"), vp=vp2)
grid.text("mu(s,t)", 0.5, unit(5, "lines"), vp=vp2)

grid.curve(grobX("h2", 180),
grobY("h2", 180),
grobX("h1", 180),
grobY("h1", 180),
shape=1, ncp=10,
square=FALSE,
curvature=.4,
arrow=arrow(angle=20,ends="first") )

upViewport()



%%%%%

for this line:
grid.text("mu(s,t)", 0.5, unit(5, "lines"), vp=vp2)

how do I change "mu(s,t)" to the expression "mu"?
I have tried 
grid.text(expression="mu(s,t)", 0.5, unit(5, "lines"), vp=vp2)
grid.text(expression(mu(s,t)), 0.5, unit(5, "lines"), vp=vp2)

both didnt work

AND

when I tried to save the output as PDF file

it returns:

Error in function (name)  : Grob 'h2' not found

I have no idea what to do?


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