Re: Tcl precision [was: Re: [Plplot-devel] Java changes to support plsurf3d()]

[Alan W. I. <ir...@be...>]

On Tue, 15 Oct 2002, [iso-8859-1] Jo=E3o Cardoso wrote:

> On Tuesday 15 October 2002 16:22, Alan W. Irwin wrote:
> | On Tue, 15 Oct 2002, [iso-8859-1] Jo=E3o Cardoso wrote:
> | > On Tuesday 15 October 2002 02:23, Alan W. Irwin wrote:
> | > |  Other non-visual
> | > | differences between the examples also show up for ifshade =3D=3D 5.
> | >
> | > What differences?
> |
> | They show up with the diff command on a psc files written with tcl,
> | C, and python front ends, but (unlike the ifshade=3D=3D1 results where
> | you see a blue edge for Python and C and no blue edge for tcl) I
> | cannot spot anything visually.
>
> Hi,
>
> I don't' want to interrupt you now, but I might forget the subject.

I don't mind short interruptions at all because they provide a welcome
break. It is just I cannot afford to spend a long time at anything to do
with PLplot at the moment.

>
> Tcl store values as strings, and there is some loss of precision with
> this process. This issue has already been discussed in this list, but
> unfortunately the mailing list archiver at sf.net does not have a
> search facility to found the thread.
> As a matter of fact, x08.tcl already has a numeric problem, that I have
> "fixed" by adding a small constant -- it is documented in the code.

As I recall the result of that thread, Maurice implemented something like 1=
2
(or 13?) significant digits as a stop-gap measure to the tcl precision
problems.  There was some reason why he did not want to increase the
precision to 17 digits.  In any case, he had a better solution in mind,
which I don't think has been implemented yet.

>
> | Once all the recently introduced memory management problems shown by
> | valgrind are fixed,
>
> Well, I have identified the problem, and "hacked" plot3d.c in order to
> correct it -- it is an index problem. But the problem is not really
> solved, it is only not apparent visually :(

I checked again with valgrind (see my previous post), and there is an
uninitialized variable in plot3d that is very likely the source of the
remaining example 8 differences between the various front ends.  I believe
this uninitialized variable is recently introduced because I did not spot
this problem when I ran valgrind extensively on example 8 right after Gary
Bishop fixed the egregious example 8 bug that had been plaguing us for such
a long time.

Alan