```
x <- seq(0, 1, by=0.2)
y <- c(1, 2, 3)
(M <- meshgrid(x, y))
gradient(M$X^2 + M$Y^2)
gradient(M$X^2 + M$Y^2, x, y)
## Not run:
# # One-dimensional example
# x <- seq(0, 2*pi, length.out = 100)
# y <- sin(x)
# f <- gradient(y, x)
# max(f - cos(x)) #=> 0.00067086
# plot(x, y, type = "l", col = "blue")
# lines(x, cos(x), col = "gray", lwd = 3)
# lines(x, f, col = "red")
# grid()
#
# # Two-dimensional example
# v <- seq(-2, 2, by=0.2)
# X <- meshgrid(v, v)$X
# Y <- meshgrid(v, v)$Y
#
# Z <- X * exp(-X^2 - Y^2)
# image(v, v, t(Z))
# contour(v, v, t(Z), col="black", add = TRUE)
# grid(col="white")
#
# grX <- gradient(Z, v, v)$X
# grY <- gradient(Z, v, v)$Y
#
# quiver(X, Y, grX, grY, scale = 0.2, col="blue")
# ## End(Not run)
```

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