How to get expression (cos (alpha)) in labels?

Question

I am trying to get a shortcut on an arrow that says:

|| x || cos (alpha)

But I can’t make it work.

I can write ||x|| no problem, and cos (alpha) no problem, but I don’t know how to include them in one operator.

Any ideas?

Here is my code:

 library(plotrix) library(shape) xlim <- c(-2, 6) ylim <- c(-2, 6) plot(0, type = "n", xlim = xlim, ylim = ylim,asp=1) Arrows(1,1,5,1) boxed.labels(3,1,labels="||x|| cos (a)",border=NA,xpad=1,ypad=1) Arrows(1,2,5,2) boxed.labels(3,2,labels=expression(cos (alpha)),border=NA,xpad=1,ypad=1) 

Answer 1

help("plotmath") and the demo.

 plot(0, type = "n", xlim = xlim, ylim = ylim,asp=1) text(2,1,labels=expression(group("||", x, "||") %.% cos(alpha)),adj=c(1.2,-1.5)) text(2,3,labels=expression(group("||", x, "||") ~ cos(alpha)),adj=c(1.2,-1.5)) 

Answer 2

You can also use bquote :

 plot(1, type = "n") text(1, 1, bquote("||x||" ~ cos(alpha))) 

Answer 3

To do this, inserted elements of expression are executed. For instance:

 plot.new() plot.window(xlim=c(0, 1), ylim=c(0, 1)) text(0.5, 0.5, expression(paste("||x|| cos(", alpha, ")")))