Re: loop bug or feature?

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

On 13/12/15 16:56, Juhász Péter wrote:
> On Sun, 2015-12-13 at 15:14 +0000, pl...@pi... wrote:
>> Hi,
>>
>>
>> I need to plot a series of data files and one reference file.
>>
>>
>> here I get all the data files and one test plot
>>
>> plot[0:1.2] for [ len=9000:7000:-50 ] s=0 \
>> , "data-".sprintf("%d",len).".out" u (1/$4):5 w l tit
>> sprintf("%d",len).".out" \
>> , "test_filter.out" u (1/$4):($5*1.5e08) w l tit " filter resp " \
>>
>>
>> but this way around I get the test plot n time and only the last data
>> file plotted.
>>
>>
>> plot[0:1.2]  for [ len=9000:7000:-50 ] s=0 \
>> , "test_filter.out" u (1/$4):($5*1.5e08) w l tit " filter resp " \
>> , "data-".sprintf("%d",len).".out" u (1/$4):5 w l  tit
>> sprintf("%d",len).".out" \
>>
>
> The plot and splot commands accept a comma-separated list of functions
> or datafiles (or variable assignments), and the for clause counts *per
> function/datafile*.
> So your command essentially sets s = 0 many times, then plots your two
> datafiles once.

No so , reread what I reported. In both cases I got multiple but 
different plots.

>
> If you omit that s=0 from your first command (it seems to be superfluous
> anyway), it will do what you want. You might want to reindent the
> command to show that the for clause belongs to a specific datafile, not
> the entire command:
>
> plot[0:1.2] \
> for [ len=9000:7000:-50 ] "data-".sprintf("%d",len).".out" u (1/$4):5 w
> l tit sprintf("%d",len).".out", \
> "test_filter.out" u (1/$4):($5*1.5e08) w l tit " filter resp"
>
>


Firstly the s=0 syntactically superfluous but it's a trick I use make 
all following lines have the same format ( beginning with a comma; end 
in escape char  ) , this means I can change line order or add/remove 
lines without tiresome editing for syntax.

>>
>>
>> gnuplot> help for
>>
>>    The `plot`, `splot`, `set` and `unset` commands may optionally contain an
>>    iteration for clause.  This has the effect of executing the basic command
>>    multiple times, each time re-evaluating any expressions that make use
>> of the
>>    iteration control variable.
>>
>>
>
> This section does not mention the fact that the for clause affects just
> one element of the plot list, however, the "help for loops" subtopic
> does:

Ah indeed:

"The scope of an iteration ends at the next comma or the end of the command,
  whichever comes first. "

So this explains why the s=0 does not affect it. There is not yet any 
substitution so there's not yet question of stopping at the " next" comma .

This does explain the difference in my two results which are then 
consistent with the help description.

There probably should at least be a "see loops" . I did "more" until the 
end of help on 'for' but since I had found the description of syntax I 
was seeking,  I did not go into the subtopics.

Many thanks for the reply, Peter.

>
>
>   This will plot one curve, sin(3x), because iteration ends at the comma
>         plot for [i=1:3] j=i, sin(j*x)
>   This will plot three curves because there is no comma after the
> definition of j
>         plot for [i=1:3] j=i sin(j*x)
>
>
>>
>> This does not seem consistent with what happens.
>>
>> regards, Peter.
>>
>>
>>
>>
>
> Peter Juhasz
>
>
>
>