# Che cosa appare? Carica tutto ed esegui.
h <- function(x,y) x^3-y^2+1
x1 <- -3; x2 <- 5; y1 <- -4; y2 <- 4
x <- seq(x1,x2,len=1000); y <- seq(y1,y2,len=1000)
z <- outer(x,y,h);contour(x,y,z,levels=0,drawlabels=FALSE, lwd=3,col='blue',asp=1)
abline(h=axTicks(2), v=axTicks(1),lty=3,col='blue')
abline(h=0, v=0,lty=2,col='blue')
r <- function(x,y) (x-1)^2+(y-1.5)^2-5
z <- outer(x,y,r);contour(x,y,z,levels=0,drawlabels=FALSE, lwd=3,col='red',add=TRUE)
k <- function(x,y) (x/y)^2-1
z <- outer(x,y,k);contour(x,y,z,levels=0,drawlabels=FALSE, lwd=3,col='brown',add=TRUE)
t <- function(x,y) x*y-x^2+y^2/3+1-x/2
z <- outer(x,y,t);contour(x,y,z,levels=0,drawlabels=FALSE, lwd=3,col='green',add=TRUE)
#
# ALTERNATIVA:
#
source("http://macosa.dima.unige.it/r.R")
BF=4; HF=4
PLANE(-3,5, -4,4)
h <- function(x,y) x^3-y^2+1;           CURVE(h,"blue")
r <- function(x,y) (x-1)^2+(y-1.5)^2-5; CURVE(r,"red")
k <- function(x,y) (x/y)^2-1;           CURVE(k,"brown")
t <- function(x,y) x*y-x^2+y^2/3+1-x/2; CURVE(t,"green")
#