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Matrix Row Echelon Form in R

For reasons unknown, I can’t find a function to transform a matrix into row echelon form in R. There’s a function on Rosetta Code for reduced row echelon form in R. So I wrote this on Sunday. And if you look at this and the Rosetta Code solution, they work in mostly the same way. This will be released as part of a larger package later, with documentation and unit tests. But it’s useful enough to stand on its own here.

refmatrix <- function(m) {
    count.rows <- nrow(m)
    count.cols <- ncol(m)
    piv <- 1
    
    for(row.curr in 1:count.rows) {
        if(count.cols > piv) {
            i <- row.curr
            while(m[i, piv] == 0) {
                i <- i + 1
                if(count.rows == i) {
                    i <- row.curr
                    piv <- piv + 1
                    if(count.cols == piv)
                        return(m)
                }
            }
            m <- swaprows(m, row.curr, i)
            for(j in row.curr:count.rows)
                if(j != row.curr) {
                    k <- m[j, piv] / m[row.curr, piv]
                    m <- replacerow(m, row.curr, j, k)
                }
            piv <- piv + 1
        }
    }
    return(m)
}

swaprows <- function(m, row1, row2) {
    row.tmp <- m[row1,]
    m[row1,] <- m[row2,]
    m[row2,] <- row.tmp

    return(m)
}

replacerow <- function(m, row1, row2, k) {
    m[row2,] <- m[row2,] - m[row1,] * k
    return(m)
}

Image by Frédérique Voisin-Demery.