Nothing
# program spuRs/resources/scripts/fixedpoint_show.r
# loadable spuRs function
fixedpoint_show <- function(ftn, x0, xmin = x0-1, xmax = x0+1) {
# applies fixed-point method to find x such that ftn(x) == x
# x0 is the starting point
# subsequent iterations are plotted in the range [xmin, xmax]
# plot the function
x <- seq(xmin, xmax, (xmax - xmin)/200)
fx <- sapply(x, ftn)
plot(x, fx, type = "l", xlab = "x", ylab = "f(x)",
main = "fixed point f(x) = x", col = "blue", lwd = 2)
lines(c(xmin, xmax), c(xmin, xmax), col = "blue")
# do first iteration
xold <- x0
xnew <- ftn(xold)
lines(c(xold, xold, xnew), c(xold, xnew, xnew), col = "red")
lines(c(xnew, xnew), c(xnew, 0), lty = 2, col = "red")
# continue iterating while user types "y"
cat("last x value", xnew, " ")
continue <- readline("continue (y or n)? ") == "y"
while (continue) {
xold <- xnew;
xnew <- ftn(xold);
lines(c(xold, xold, xnew), c(xold, xnew, xnew), col = "red")
lines(c(xnew, xnew), c(xnew, 0), lty = 2, col = "red")
cat("last x value", xnew, " ")
continue <- readline("continue (y or n)? ") == "y"
}
return(xnew)
}
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