special symbols on R plot

Sometimes we need put special symbols, like Greek letters and italic type, on the plots. Sometimes, we also want to put mathematical annotation on the plot. In R we can use the function expression() do this job:

Sample codes

xlab.name = expression(paste(italic(vti), Delta, sep=""))
ylab.name = expression(mu * "ml")
main.name = expression(paste(plain(sin) * phi))
plot(0, 0, xlab=xlab.name, ylab=ylab.name, main=main.name, xlim=c(-pi, pi), ylim=c(-1.5, 1.5), axes=FALSE)
axis(1, at = c(-pi, -pi/2, 0, pi/2, pi), labels = expression(-pi, -pi/2, 0, pi/2, pi))
axis(2)
box()
text(-pi/2, 0, expression(hat(alpha) == (X^t * X)^{-1} * X^t * y))
text(pi/2, 0, expression(paste(frac(1, sigma*sqrt(2*pi)), plain(e)^{frac(-(x-mu)^2, 2*sigma^2)}, sep="")), cex = 1.2)

### #######################
PS: for the subscript expression,
We should use
> ylab.name = expression(sigma[21])

############################
There are webpages talking about this issue in details. Mathematical Annotation in R: http://rweb.stat.umn.edu/R/library/grDevices/html/plotmath.html
##############################
others:
main=expression(paste(italic(Sch9), Delta, " (18s and 5.8s)")),

However, if we want to use a variable in the expression, we should use substitute:
e.g.

n <- 20
plot(0, 0, main = substitute(paste(n[i], " = ", k), list(k = n)));
i=2;
range.name = substitute(paste(italic(Sch9), Delta, " ", p, "/", k, " hr"), list(k = i*12, p = (i+1)*12));
text(0, 0, range.name)
# with a variable, we can use for iteration to produce multiple tags
##############################

Plot in details

When we plot, we can assign the plot title, label.
We can also choose to show axis or not. On axis, we can set notations' letter size by cex.axis, direction by las.


Sample codes:

image.data = matrix(rnorm(60), nrow=10, ncol=6)
windows()
par(mar=c(5, 5, 4, 1))
image(x=1:nrow(image.data), y=1:ncol(image.data), image.data, axes = FALSE, xlab="X", ylab = "Y", main = "SAMPLE")
par(las=2) #control word's direction on plot, las = 1 or 2
namess1 = paste("row", 1:ncol(image.data), sep="-")
axis(2, 1:ncol(image.data), namess1, cex.axis=0.9, tick = FALSE)
par(las=2)
namess2 = paste("col", 1:nrow(image.data), sep="-")
axis(1, 1:nrow(image.data), namess2, cex.axis=0.9, tick = TRUE)
box()



windows()
par(mar=c(5, 5, 4, 1))
boxplot(data.frame(image.data), axes = FALSE, xlab="cols", ylab = "Distribution", main = "SAMPLE")
axis(2, tick = TRUE)
par(las=1)
namess2 = paste("col", 1:nrow(image.data), sep="-")
axis(1, 1:nrow(image.data), namess2, cex.axis=0.9, tick = TRUE)
box();