Re: floating point, step forward issue, Manipulate Appearance
- To: mathgroup at smc.vnet.net
- Subject: [mg108785] Re: floating point, step forward issue, Manipulate Appearance
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Wed, 31 Mar 2010 05:28:17 -0500 (EST)
Ah, the incompatibility of binary computer representation of numbers and
the decimal representation modern humans prefer!
Try Chop.
On 3/30/2010 6:02 AM, Nasser M. Abbasi wrote:
> Consider the following:
>
> Manipulate[Null, {{a, -0.1, "a"}, -0.1, 0.1, 0.1, Appearance ->
> "Labeled"}]
>
> Now click on the little "+" button at the end of the slider near the number
> ".1" to open the animation controls. Now click on the "play" button, You
> should see nothing too exciting, just a sequence of number
> {-.1,0,.1,-.1,0,.1,....} as expected.
>
> Now try the same as above, but change the range to be -0.3,0.3,0.1, as
> follows
>
> Manipulate[Null, {{a, -0.1, "a"}, -0.3, 0.3, 0.1, Appearance ->
> "Labeled"}]
>
> and run it again with the play button, now you'll see this output:
>
> {-0.3,-0.2,-0.1, 8.32667*10^-17 ,0.1,0.2,0.3,.... and it repeats}. This is
> the same output one gets by doing
> Range[-.3, .3, .1]
>
> So, to avoid the floating point display problem on the label of the control,
> I changed the code to do a step by exact fraction values as follows:
>
> Manipulate[Null, {{a, -1/10, "a"}, -3/10, 3/10, 1/10, Appearance ->
> "Labeled"}]
>
> and when the above is played, you'll see that the exact values are stepped
> over as I wanted. No floating point hickups.
>
> The problem, is that I do not want to display the values as fractions on the
> slider label, but as decimals. I am talking about the label itself, on the
> end of the slide, which shows the control value of the control variable. Now
> this is shown as 1/10, 2/10, etc...
>
> So, I changed the above to the following:
>
> Manipulate[Null,{{a,-N[1/10],"a"},-N[3/10],3/10,1/10,Appearance->"Labeled"}]
>
> And now, it displays as decimal points on the label, and also I do not get
> the floating point leftovers displayed anymore when it steps forward.
>
> I was wondering if there is a better solution than having to throws N's here
> and there to get it to work as expected. I wanted to put one N[] around the
> control variable itself, like this:
>
> Manipulate[Null,{{N[a],-1/10,"a"},-3/10,3/10,1/10,Appearance->"Labeled"}]
>
> But I can't ofcourse. N[a] is not valid symbol anymore. The better solution
> would have been is to capture what goes to the label, so I can format it as
> I want. It would be nice to be able to do this. I.e. when one types
>
> Appearance -> "Labeled"
>
> on a control, there is now no way to intercept this label, or tell
> Mathematica how to format it. At least, I did not find a way. If there was,
> I could have written something like this
>
> Manipulate[Null, {{a, -0.1, "a"}, -0.3, 0.3, 0.1, Appearance ->
> {"Labeled", N[#]& }] % not valid code
>
>
> Thanks,
> --Nasser
>
>
>
--
Murray Eisenberg murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2859 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305