When X and Y are independent standard normal random variables, their joint probability density function (PDF) has contours in the shape of circles. The contours become ellipses for bivariate normal distribution with non-zero correlation. Consider the case in which X and Y are Laplace random variables.

1) How to draw the contour line the joint PDF for independent Laplace random variables X and Y with theta = 1 by R code?

2) How to draw the joint PDF in a 3-D graph by R?