poly2str.R
##
## p o l y 2 s t r . R Print Polynomial
##
poly2str <- function(p, svar = "x", smul = "*",
d = options("digits")$digits) {
if (length(p) == 0) return("")
if (!is.numeric(p))
stop("Argument 'p' must be a numeric vector.")
while (p[1] == 0 && length(p) > 1)
p <- p[2:length(p)]
if (length(p) == 1) return(as.character(p))
s <- sign(p)
p <- abs(p)
p <- formatC(p, digits = d)
p <- sub("^\\s+", "", p) # p <- pracma::strtrim(p)
n <- length(p) - 1
S <- ""
s1 <- if (s[1] == 1) "" else "-"
S <- paste(s1, p[1], smul, svar, "^", n, sep = "")
for (i in 2:(n+1)) {
if (s[i] == 1) s1 <- " + "
else if (s[i] == -1) s1 <- " - "
else next
if (n-i+1 > 1) {
S <- paste(S, s1, p[i], smul, svar, "^", n-i+1, sep="")
} else if (i == n) {
S <- paste(S, s1, p[i], smul, svar, sep="")
} else {
S <- paste(S, s1, p[i], sep="")
}
}
return(S)
}