The R Project SVN R

\name{plotmath}
\alias{plotmath}
\title{Mathematical Annotation in R}
\description{
  If the \code{text} argument to one of the text-drawing functions
  (\code{\link{text}}, \code{\link{mtext}}, \code{\link{axis}}) in \R
  is an expression, the argument is interpreted as a mathematical
  expression and the output will be formatted according to TeX-like
  rules.
}
\details{
  A mathematical expression must obey the normal rules of syntax for any
  \R expression, but it is interpreted according to very different rules
  than for normal \R expressions.
  
  \describe{
    \item{\emph{Binary operators:}}{
      addition, subtraction, multiplication, and division use the
      standard \R syntax, although multiplication only juxtaposes the
      arguments.
      
      For example, \code{a+b}, \code{a-b}, and \code{a/b}, produce
      \eqn{a+b}, \eqn{a-b}, and \eqn{a/b}, but \code{a*b} produces
      \eqn{ab}.}
    
    \item{\emph{Unary operators:}}{
      positive and negative numbers are specified with standard syntax.
      
      For example, \code{+x} produces \eqn{+x} and \code{-y} produces
      \eqn{-y}.}
    
    \item{\emph{Subscripts and superscripts:}}{
      a subscript is specified using the subsetting syntax and a
      superscript is specified using the power syntax.
      
      For example, \code{x[i]} produces \eqn{x_i} and \code{x^2}
      produces \eqn{x^2}.}
    
    \item{\emph{Accents:}}{
      accented expressions are specified using the special mathematical
      functions \code{hat} and \code{bar}.}
    
    % For example, \code{hat(x)} produces \eqn{\hat{x}} and \code{bar(x)}
    % produces \eqn{\bar{x}}.
    
    \item{\emph{Fractions:}}{
      fractions are specified using the special mathematical function
      \code{frac} (or its alias, \code{over}).}
    
    % For example, \code{frac(1,2)} produces \eqn{1\over2}.
    
    \item{\emph{Relations:}}{
      equality or assignment of terms is specified using the \code{==}
      relation.
      
      For example, \code{x == y} produces \eqn{x=y}.}
    
    \item{\emph{Visible grouping:}}{
      terms are visibly grouped by placing them within parentheses.
      
      For example, \code{(x+y)} produces \eqn{(x+y)}.}
    
    \item{\emph{Invisible grouping:}}{
      terms are invisibly grouped by placing them within curly braces.

      For example, \code{x^{2*y}} produces \eqn{x^{2y}}, whereas
      \code{x^2*y} produces \eqn{x^2y}.}

    \item{\emph{Big operators:}}{
      a sum, product, or integral is specified using the special
      mathematical function of the corresponding name.  Each of these
      functions takes three arguments;  the first indicates what is
      being summed/multiplied/integrated and the second and third
      specify the limits of the summation/product/integral.
      
      For example, \code{sum(x[i], i==0, n)} produces
      \deqn{\sum\limits_{i=0}^n x_i}{sum_{i=0}^n x_i}}

    \item{\emph{Radicals:}}{
      a square root expression is specified using the special
      mathematical functions \code{root} and \code{sqrt}.}
      
    % For example, \code{sqrt(x)} produces \eqn{\sqrt x}.

    \item{\emph{Absolute values:}}{
      an absolute term is specified using the special mathematical
      function \code{abs}.

      For example, \code{abs(x)} produces \eqn{|x|}.}

    \item{\emph{Juxtaposition:}}{
      multiple terms are juxtaposed using the special mathematical
      function \code{paste}.
      
      For example, \code{paste(over(b, 2), y, sum(x))} produces
      \eqn{\frac{b}{2} y \sum x}{b/2 y sum(x)}.}
   
    \item{\emph{Typeface changes:}}{
      the default font in mathematical expressions is italic (except for
      terms which are symbols).  A new typeface is specified using the
      special mathematical functions \code{bold}, \code{italic},
      \code{plain}, and \code{bolditalic}.  Note that these font
      specifications do not accumulate (i.e., \code{bold(italic(x)))}
      gives an italic `x', whereas \code{bolditalic(x)} produces a bold,
      italic `x').}

    \item{\emph{General expressions:}}{
      any functional expression which is not a special mathematical
      function is simply reproduced as a function expression.

      For example, \code{foo(x)} produces \eqn{foo(x)}.}
  }
}
\seealso{
  \code{\link{axis}},
  \code{\link{mtext}},
  \code{\link{text}},
  \code{\link{title}}
}
\examples{
x <- seq(-4, 4, len = 101)
y <- cbind(sin(x), cos(x))
matplot(x, y, type = "l", xaxt = "n",
        main = expression(paste(plain(sin) * phi, "  and  ",
                                plain(cos) * phi)),
        ylab = expression("sin" * phi, "cos" * phi), # only 1st is taken
        xlab = expression(paste("Phase Angle ", phi)),
        col.main = "blue")
axis(1, at = c(-pi, -pi/2, 0, pi/2, pi),
     lab = expression(-pi, -pi/2, 0, pi/2, pi))

plot(1:10, 1:10)
text(4, 9, expression(hat(beta) == (X^t * X)^{-1} * X^t * y))
text(4, 8.4, "expression(hat(beta) == (X^t * X)^{-1} * X^t * y)",
     cex = .8)
text(4, 7, expression(bar(x) == sum(frac(x[i], n), i==1, n)))
text(4, 6.4, "expression(bar(x) == sum(frac(x[i], n), i==1, n))",
     cex = .8)
text(8, 5, expression(paste(frac(1, sigma*sqrt(2*pi)), " ",
                            plain(e)^{frac(-(x-mu)^2, 2*sigma^2)})),
     cex= 1.2)
}
\keyword{aplot}