At 4:40 PM +0000 10/25/01, Joshua Zucker wrote:

>Anyway, right now my issue is that I'm trying to do some tricky

>arithmetic with floor functions. It graphs things like x - floor(x)

>beautifully, except for drawing in the vertical lines where a human

>would draw open or closed circles, but that's OK.

>

>It has HUGE problems with things like floor(x-floor(x)) when x is

>near an integer ... it can't tell whether the answer is 1 or -1, so it

>graphs funny vertical lines.

>

>This really makes it hard to tell whether my function is doing

>what I want it to do, because those points are exactly the ones

>I'm interested in.

Hi Josh,

This artifact is due to a bug/design-flaw in the underlying interval

arithmetic which does not handle discontinuous functions well.

GrafEq from www.peda.com does a much better job drawing functions like this.

In Graphing Calculator, you can switch an equation to "simple plotting" mode

which does not use the interval arithmetic and will just compute the

value at each point and connect the dots. This should handle these cases

better. (However, cases where the function varies rapidly such as sin(e^x)

will break down.)

To switch mode, select the equation you want to affect, then:

Command-option-s (simple plotting)

Command-option-b (the version 3 default mode using interval arithmetic)

Command-option-h (the version 1 Honest Plotting mode using interval

arithmetic)

>I can see why it would have trouble there (a tiny change in one of

>the two x's in my function could easily cause the function to flip

>from 1 to 0 to -1) ... is there any chance this behavior will improve

>in later versions, or is this just part of the way the graphing

>engine deals with things?

I'll put this on the list of problems to be addressed in a future release.

Best regards,

Ron