Re: data and function plot causing double assignment

[Ethan M. <merritt@u.washington.edu>]

On Tuesday, October 04, 2011 10:03:10 am pl...@pi... wrote:
> On 10/04/11 18:22, Ethan Merritt wrote:
> > On Tuesday, October 04, 2011 08:43:02 am pl...@pi... wrote:
> >> On 10/04/11 17:28, Ethan Merritt wrote:
> >>> On Tuesday, 04 October 2011, pl...@pi... wrote:
> >>>> Hi,
> >>>>
> >>>> I have found what appears to be a defect in variable assignments in plot.
> >>>>
> >>>> gauss0(x)=a0*exp(-(x-pk0)**2/b0)+c0
> >>>> a1=a0;b1=b0;c1=c0;pk0=-141;
> >>>> add_one(x)=area0=1;
> >>>
> >>> This defines the function add_one(x)
> >>> to be  add_one(x) =   value of (area0=1)
> >>>                     = 1
> >>> So add_one(x) = 1 for all x
> >>
> >> Exactly, so why is area still 0 after having been assigned the value 1
> >> about 512 times?!
> >
> > Ah. I thought you were asking about the behaviour of add_one(),
> > since its name implies that it performs an addition but in fact it
> > is defined to always equal 1.  I wondered if you didn't simply have
> > a typo for   "add_one_x = area0 +1".
> > Anyhow...
> >
> >> I reiterate that if I remove the function plot I do get areas=1 after
> >> plotting. This indicates that plot is re-executing area0=0 after the
> >> second data plot and before plotting the function.
> >
> > I don't say this is good/bad, expected/unexpected, bug/feature, or simply
> > confusing, but this is the way it has always worked.  Each plot command
> > is evaluated once to detect functions, read in data, and determine plot
> > ranges; then it is evaluated again to fill in function values over the
> > now-determined range; then it is plotted.   If there are no functions then
> > the second of those three operations is skipped.
> >
> > See also
> >    https://sourceforge.net/tracker/index.php?func=detail&aid=2907028&group_id=2055&atid=102055
> >
> > 	Ethan
> > #
> Thanks ,  I can understand that bug report and how your explanation 
> above accounts for what was reported. However, it does not seem to 
> explain what I'm seeing.
> 
> Is the order perhaps:
> evaluate
> plot data
> evaluate
> plot functions
> ?

Nope.    
Code snippetes from plot2d.c

    /* ** First Pass: Read through data files ***
     * This pass serves to set the xrange and to parse the command, as well
     * as filling in every thing except the function data. That is done after
     * the xrange is defined.
     */
[...]
/*** Second Pass: Evaluate the functions ***/
    /*
     * Everything is defined now, except the function data. We expect
     * no syntax errors, etc, since the above parsed it all. This
     * makes the code below simpler. If y is autoscaled, the yrange
     * may still change.  we stored last token of each plot, so we
     * dont need to do everything again */
[...]
    if (some_functions) {
[...]
    }   /* some_functions */
[...]

    if (table_mode) {
        print_table(first_plot, plot_num);

    } else {
        /* do_plot now uses axis_array[] */
        do_plot(first_plot, plot_num);
    }


-- 
Ethan A Merritt
Biomolecular Structure Center,  K-428 Health Sciences Bldg
University of Washington, Seattle 98195-7742