diagram package; plotmat function

[nikk]

Is there any way to change the direction of the arrows in the plotmat function?

library(diagram)

abcd <- matrix(c("a", "b", "c", "d"), nrow = 2, byrow = TRUE)
abcd

ab <- c("A","B")
row.names(abcd) <- ab; colnames(abcd) <- ab
par(new = TRUE)
plotmat(abcd, pos = c(1,1), 
        lwd = 1, box.lwd = 2, 
        cex.txt = 0.8, 
        box.cex = 1.5,
        box.size = 0.1, 
        box.type = "circle", 
        box.prop = 0.5,
        box.col = "white",
        box.lcol = "black",
        arr.col = "black",
        arr.type = "triangle",
        arr.length=.3,
        arr.width=.2,
        self.cex = .6,
        self.shifty = -.01,
        self.shiftx = .16)

I want the arrow for c to point upward and vice versa. Is there any way to do this?

I've also posted the question on reddit:
https://www.reddit.com/r/rprogramming/comments/ghyqfw/diagram_package_plotmat_function/

[nikk]

I solved it! I added arr.pos and set a negative value which switched the direction of the arrows.