[R] plotmath vector problem; full program enclosed

[Paul Johnson]

Here's another example of my plotmath whipping boy, the Normal distribution.

A colleague asks for a Normal plotted above a series of axes that
represent various other distributions (T, etc).

I want to use vectors of equations in plotmath to do this, but have
run into trouble.  Now I've isolated the problem down to a relatively
small piece of working example code (below).  If you would please run
this, I think you will see the problem.  When plotmath meets one
vector of expressions, it converts all but one to math, so in the
figure output i get, in LaTeX speak

b1         $\mu-1.0 \sigma$    $\mu$

All values except the first come out correctly.

This happens only when I try to use bquote or substitute to get
variables to fill in where the 1.96, 1.0, and so forth should be.  In
the figure output, you should see a second axis where all of the
symbols are resolved correctly.

As usual, thanks in advance for your help, sorry if I've made an
obvious mistake or overlooked a manual.

### Filename: plotMathProblem.R
### Paul Johnson July 5, 2010
### email me <pauljohn at ku.edu>

  sigma <- 10.0
  mu <- 4.0

  myx <- seq( mu - 3.5*sigma,  mu+ 3.5*sigma, length.out=500)

  myDensity <- dnorm(myx,mean=mu,sd=sigma)

  ### xpd needed to allow writing outside strict box of graph
  ### Need big bottom margin to add several x axes
  par(xpd=TRUE, ps=10, mar=c(18,2,2,2))

  plot(myx, myDensity, type="l", xlab="", ylab="Probability Density ",
main=myTitle1, axes=FALSE)
  axis(2, pos= mu - 3.6*sigma)
  axis(1, pos=0)

  lines(c(myx[1],myx[length(myx)]),c(0,0)) ### closes off axes


  addInteriorLine <- function(x, m, sd){
    for (i in 1:(length(x))){
      lines( c(x[i],x[i]), c(0, dnorm(x[i],m=m,sd=sd)), lty= 14, lwd=.2)
    }
  }


  dividers <- c(qnorm(0.025), -1, 0, 1, qnorm(0.975))
  addInteriorLine(mu+sigma*dividers, mu,sigma)

  # bquote creates an expression that text plotters can use
  t1 <-  bquote( mu== .(mu))
  mtext(bquote( mu == .(mu)), 1, at=mu, line=-1)


  addInteriorLabel <- function(pos1, pos2, m, s){
    area <- abs(100*( pnorm(m+pos1*s,m,s)-pnorm(m+pos2*s, m,s)))
    mid <- m+0.5*(pos1+pos2)*s
    text(mid, 0.5*dnorm(mid,m,s),label=paste(round(area,2),"%"))
  }


  addInteriorLabel(dividers[1],dividers[2],  mu, sigma)
  addInteriorLabel(dividers[2],dividers[3],  mu, sigma)
  addInteriorLabel(dividers[3],dividers[4],  mu, sigma)
  addInteriorLabel(dividers[4],dividers[5],  mu, sigma)




### Following is problem point: axis will
### end up with correct labels, except for first point,
### where we end up with "b1" instead of "mu - 1.96*sigma".
   b1 <- substitute( mu - d*sigma, list(d=round(dividers[1],2)) )
   b2 <- substitute( mu - sigma )
   b3 <- substitute( mu )
   b4 <- substitute( mu + sigma )
   b5 <- substitute( mu + d*sigma, list(d=round(dividers[5],2)) )
##   plot(-20:50,-20:50,type="n",axes=F)
   axis(1, line=4,at=mu+dividers*sigma,
labels=c(expression(b1),b2,b3,b4,b5), padj=-1)




### This gets "right result" but have to hard code the dividers
  b1 <- expression( mu - 1.96*sigma )
  b2 <- expression( mu - sigma )
  b3 <- expression( mu )
  b4 <- expression( mu + sigma )
  b5 <- expression( mu + 1.96*sigma )
  axis(1, line=8,at=mu+dividers*sigma, labels=c(b1,b2,b3,b4,b5), padj=-1)




-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas