バレンタインなのでStanで絵を描いた - Qiita

data { real<lower=0> lambda; } parameters { real x; real y; } model { target += -lambda*(x^2.0 + (y - (x^2.0)^(1.0/3.0))^2.0 - 1)^2; } library(rstan) library(ggplot2) pars <- c("x", "y") warmup <- 1000 iter <- 3000 seed <- 87 chains <- 4 src <- "heart.stan" lambda <- 100 basefit <- stan(file = src, data = list(lambda = lambda), pars = pars, seed = seed, chains = chains, warmup = warmup, iter = ite