I just pushed a change that should keep it from raising an error. Can
you get the latest and try it? If there's no error, will you please send
me (personally, not the list) a screenshot of the result?
Could you also try this?
#lang racket
(require plot racket/flonum unstable/flonum)
(plot (function sqrt 0 (* 40 +min.0)))
(plot (function (compose flsqrt exact->inexact) 0 (* 40 +min.0)))
Both plots should be identical and look like staircases.
The thing is, the error shouldn't be happening at all. As far as I can
tell, it happens because at least one surface normal of a polygon that
makes up the plot has a +nan.0 in it.
That *could* happen if your machine's floating-point processor is pretty
b0rked - for example, if it returned +nan.0 for square roots of very
small numbers. (Or possibly Racket on your machine, for some reason,
computes things like that wrongly.) Have you had floating-point problems
with anything else?
(It's not too unusual, BTW. I had a laptop where (exp 20) was wrong in
the least significant 20 bits.)
Neil T
On 12/06/2011 03:13 AM, Marijn wrote:
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So I just wanted to repost this to dev for the record.
The program:
;== start
#lang racket
(require plot)
;(plot3d-diffuse-light? #f)
;(plot3d-specular-light? #f)
(plot3d (list (surface3d (λ (x y) (+ (sqr x) (sqr y))) -1 1 -1 1
#:label "z = x^2 + y^2")
(surface3d (λ (x y) (- (+ (sqr x) (sqr y)))) -1 1 -1 1
#:color 4 #:line-color 4
#:label "z = -x^2 - y^2")))
;== end
produces:
inexact->exact: no exact representation for +nan.0
but when the commented lines are uncommented it does plot. The plot
looks plausible, though apparently it should be possible to drag
inside the plot area to change the view. This is not possible for me;
the view is stuck from looking along the xy-plane onto the z-axis.
Matthew has been trying to determine the cause via private email.
Matthew, has any of the data I provided so far pointed you anywhere?
Otherwise is there something else I can do to help debug?
Marijn
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