# [racket-dev] Plot Contour Intervals Question (Bug?)

On 08/03/2012 11:59 AM, Doug Williams wrote:
>* (require plot)
*>*
*>* (plot (contour-intervals
*>* (lambda (x y)
*>* (define z (- x y))
*>* (cond ((< z -1) -1)
*>* ((> z 1) 1)
*>* (else z)))
*>* -2 2 -2 2))
*>*
*>* ...
*>*
*>* Why is the lower white triangle not colored red - they definitely have
*>* a value of 1? It's like those points are completely ignored.
*
Turns out it was an error in the marching squares (intervals)
implementation: a `<' should have been a `<=' to make an upper test
symmetric with the corresponding lower test.
I've pushed the fix. Thanks again!
Neil ⊥