[R] arrow on contour line

[John Kane]

Something like this shodld worx.  You will need to fiddle around with the
actual co-ordinates etc. I just stuck an arrow in what seemed like a handy
place

On Wed, 10 Jan 2024 at 19:13, Deepankar Basu <basu.15 using gmail.com> wrote:

> Hello,
>
> I am drawing contour lines for a function of 2 variables at one level of
> the value of the function and want to include a small arrow in any
> direction of increase of the function. Is there some way to do that?
>
> Below is an example that creates the contour lines. How do I add one small
> arrow on each line in the direction of increase of the function (at some
> central point of the contour line)? Any direction will do, but perhaps the
> direction of the gradient will be the best.
>
> Thanks in advance.
> DB
>
> --------------------------------------------
>
> library(tidyverse)
>
> x <- seq(1,2,length.out=100)
> y <- seq(1,2,length.out=100)
>
> myf <- function(x,y) {x*y}
> myg <- function(x,y) {x^2 + y^2}
>
> d1 <- expand.grid(X1 = x, X2 = y) %>%
>   mutate(Z = myf(X1,X2)) %>%
>   as.data.frame()
>
> d2 <- expand.grid(X1 = x, X2 = y) %>%
>   mutate(Z = myg(X1,X2)) %>%
>   as.data.frame()
>
> ggplot(data = d1, aes(x=X1,y=X2,z=Z))+
>   stat_contour(breaks = c(2)) +
>   stat_contour(data=d2, aes(x=X1,y=X2,z=Z), breaks=c(6))
>
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>
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-- 
John Kane
Kingston ON Canada

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