能凑合用吗？

### f(x, y) = (x-2)^2 + (y-2)^2 + 2*y^3- 16

fr <- function(z) {
  x <- z[1]
  y <- z[2]
  abs((x-2)^2 + (y-2)^2 + 2*y^3- 16)
}

mat <- t(sapply(X = 1:20000, FUN = function(x){
  optim(c(rnorm(1),rnorm(1)), fr)$par}) )

range(mat[, 1])
range(mat[, 2])

mat <- t(sapply(X = 1:50000, FUN = function(x){
  optim(c(runif(1, range(mat[, 1])),runif(1,range(mat[, 2]))), fr)$par}) )

colnames(mat) <- c("x", "y")
dat <- data.frame(mat)

dat1 <- dat2 <- dat
dat1[dat1$x>=-2, ] <- NA   #change this when needed
dat2[dat2$x<=+6, ] <- NA #change this when needed

library(ggplot2)
ggplot(data=dat, aes(x=dat$x, y=dat$y)) +
  geom_point(size=0.05) +
  geom_line(data=dat1, aes(x=dat1$x, y=dat1$y))+
  geom_line(data=dat2, aes(x=dat2$x, y=dat2$y))

### f(x, y) = (x-2)^2 + (y-2)^2 + 2*y^3- 16

fr <- function(z) {
  x <- z[1]
  y <- z[2]
  abs((x-2)^2 + (y-2)^2 + 2*y^3- 16)
}

mat <- t(sapply(X = 1:20000, FUN = function(x){
  optim(c(rnorm(1),rnorm(1)), fr)$par}) )
colnames(mat) <- c("x", "y")
dat <- data.frame(mat)
library(ggplot2)
ggplot(data=dat, aes(x=dat$x, y=dat$y)) +
  geom_point(size=0.05)


range(mat[, 1])
range(mat[, 2])

mat <- t(sapply(X = 1:50000, FUN = function(x){
  optim(c(runif(1, range(mat[, 1])),runif(1,range(mat[, 2]))), fr)$par}) )
colnames(mat) <- c("x", "y")
dat <- data.frame(mat)

dat1 <- dat2 <- dat
dat1[dat1$x>=-2, ] <- NA
dat2[dat2$x<=+6, ] <- NA

ggplot(data=dat, aes(x=dat$x, y=dat$y)) +
  geom_point(size=0.05) +
  geom_line(data=dat1, aes(x=dat1$x, y=dat1$y))+
  geom_line(data=dat2, aes(x=dat2$x, y=dat2$y))

谢谢，学习了。