In friendly/matlib: Matrix Functions for Teaching and Learning Linear Algebra and Multivariate Statistics

knitr::opts_chunk$set(echo = TRUE)

It would be nice to add a feature to border matrices with row/col labels. Here it is done naively from scratch using nested matrix / pmatrix arrays, from https://github.com/mathjax/MathJax/issues/2031

$$
\begin{matrix}
  &  \begin{matrix} A & C & G & T    % row labels
     \end{matrix} \\
  \begin{matrix}                     % col labels
      \alpha \\ 
      \beta \\ 
      \gamma \\ 
      \epsilon
  \end{matrix}  &  
    \begin{pmatrix}                  % body
    1 & 2 & 3 & 4\\
    3 & 4 & 5 & 6\\
    3 & 4 & 5 & 6\\
    3 & 4 & 5 & 6
  \end{pmatrix}\\
\end{matrix}
$$

This produces:

A note there says: unfortunately, for some reason, the output works only when render()ing the *.Rmd to PDF (via LaTeX), not to HMTL (via Markdown). Not sure why, raised it here: http://stackoverflow.com/questions/30740613/how-do-i-get-latex-math-typeset-matrix-with-borders-in-html-output-from-rmd

Answer: FYI, MathJax currently does not support \bordermatrix because it does not (yet) support columspan/rowspan from the MathML spec (which is our internal format). See also https://github.com/mathjax/MathJax/issues/1127 Peter Krautzberger Commented Jun 22, 2015 at 15:56

A function?

Another SO discussion, https://stackoverflow.com/questions/20749444/converting-r-matrix-into-latex-matrix-in-the-math-or-equation-environment gives this function:

borderMatrix <- function(matr) {
    matr <- round(x = matr, digits = 2)  # sadly this is necessary because given this function, the options(digits = 2) does not work
    matr2 <- data.frame(c("~",rownames(matr)))  # add rownames
    for (r in colnames(matr)) {  # add col contents and colnames
      matr2 <- cbind(matr2, c(r, matr[,r]))
    }
    printmrow <- function(x) {
        ret <- paste(paste(x, collapse = " & "), "\\cr")
        sprintf(ret)
    }
    out <- apply(matr2, 1, printmrow)
    out2 <- paste("\\bordermatrix{", paste(out, collapse = ' '),"}")
    return(out2)
}

Which uses this LateX macro:

\newcommand{\bordermatrix}[3]{%
  \begin{matrix} & %
    \begin{matrix}#1 %       row labels
    \end{matrix} \\\\ %
    \begin{matrix}#2 %       col labels
    \end{matrix} %
    \hspace{-1em} & #3 %     body
  \end{matrix}}

In this document, the above is inserted using $$ .. $$. $$ \newcommand{\bordermatrix}[3]{% \begin{matrix} & % \begin{matrix}#1 % \end{matrix} \\ % \begin{matrix}#2 % \end{matrix} % \hspace{-1em} & #3 % \end{matrix}} $$

The macro is used as:

\bordermatrix{A & C & G & T }%
             {\alpha \\  \beta \\  \gamma \\ \epsilon}%
  { 
  \begin{pmatrix}                  % body
    1 & 2 & 3 & 4\\
    3 & 4 & 5 & 6\\
    3 & 4 & 5 & 6\\
    3 & 4 & 5 & 6
  \end{pmatrix}\\
  }

Testing the function:

mat <- matrix(1:16, nrow=4)
rownames(mat) <- c("\\alpha", "\\beta", "\\gamma", "\\epsilon")
colnames(mat) <- LETTERS[1:4]

borderMatrix(mat)

Trying to render the result:

borderMatrix(mat)

friendly/matlib documentation built on Dec. 6, 2024, 9:25 a.m.