#A function that is sometimes useful in determining the

#coordinate(i.e. row and column number) of a matrix position

#(and vice-versa).

#Either a vector of positions ("pos")

#OR a 2 column matrix of matrix coordinates, ("coord", i.e. cbind(row,col)),

#AND the matrix dimentions must be supplied (dim.mat, i.e. c(nrow,ncol)).

pos2coord<-function(pos=NULL, coord=NULL, dim.mat=NULL){

if(is.null(pos) & is.null(coord) | is.null(dim.mat)){

stop("must supply either 'pos' or 'coord', and 'dim.mat'")

}

if(is.null(pos) & !is.null(coord) & !is.null(dim.mat)){

pos <- ((coord[,2]-1)*dim.mat[1])+coord[,1]

return(pos)

}

if(!is.null(pos) & is.null(coord) & !is.null(dim.mat)){

coord <- matrix(NA, nrow=length(pos), ncol=2)

coord[,1] <- ((pos-1) %% dim.mat[1]) +1

coord[,2] <- ((pos-1) %/% dim.mat[1]) +1

return(coord)

}

}

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