I've replied to the list because this might be useful for other people.
On 05/22/2012 02:41 AM, Jens Axel Søgaard wrote:
Hi Neil,
I am attempting to draw 1/x in using plot.
Ideally I'd like to be able to write:
(lambda (x) (if (zero? x) #f (/ x))
in order to plot a function with singularities.
I've thought of such things before. Unfortunately, plot doesn't know
where any singularities are, so it can't specifically sample the
function at those points. I could probably allow the user to tell plot
where they are, but I can't think of a good API for it. I'd want
something general enough to handle 1D, 2D and 3D functions, which allows
the user to specify countably many missing values, and direction of
(dis)continuity.
Since the contract for plot requires I must use numbers,
I attempted to split the domain in two from -1 to -epsilon
and from +epsilon to 1.
That trick didn't work (see attached image).
Am I missing something?
You're not missing anything. There's currently a problem with the
renderers returned by `function', `surface3d' and others: they sample
functions on the entire plotted domain, not just within the functions'
stated domains. To split a function in half and not have it draw a line
between the halves, you currently have to do something like this:
(plot (list (function (λ (x) (if (x . < . 0) (/ x) +nan.0)) -2 0)
(function (λ (x) (if (x . > . 0) (/ x) +nan.0)) 0 2)))
This also causes performance problems when there are many small function
renderers. Fixing it is next on my to-do list.
Apropos something completely different:
At the page "Introduction" it would be nice if
the first example included (require plot).
http://docs.racket-lang.org/plot/intro.html?q=plot
Duly noted.
Neil ⊥
____________________
Racket Users list:
http://lists.racket-lang.org/users
