Re: data and function plot causing double assignment

[<pl...@pi...>]

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
?
regards.



>> /Peter.
>>
>>
>>> Any later changes to the value of area0 are not relevant.
>>>
>>> 	Ethan
>>>
>>>> plot  area0=0\
>>>> , datafile using 1:(add_one($2)) w l\
>>>> , datafile using 1:(($2)) w l\
>>>> , gauss0(x) tit 'fitted peak0'\
>>>>
>>>> print "area0=",area0;
>>>>
>>>> I was expecting this to do the assignment area0=0 once and once only
>>>> before any of the lines were plotted.
>>>>
>>>> It is only assigned once for the datafile plots but adding the function
>>>> plot causes this snippet to print a value of zero , not one.
>>>>
>>>> I am inferring that using a mix of data and function plots is causing
>>>> the initial assignment to be done twice.  Bug or feature?
>>>>
>>>> best regards, Peter.
>>>>
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>>>
>>>
>>
>>
>