[Scilab-Dev] new logflags syntax of plot() in 6.1

[Samuel Gougeon]

Dear Stéphane,

This thread was on Bugzilla for more than 4 years, and the commit was on 
review for a full year.

This feature is completely back-compatible. It breaks nothing.
About any "spirit" : The only one that i know -- and it has always been 
very explicit -- is to improve Scilab by all possible and relevant ways.
IMHO in no way considering Scilab as a museum of features coming from 
anywhere else, or even internal, as in a showcase preventing any 
forthcoming changes -- could be considered as a way for improving Scilab.

The new "logflags" argument is actually badly named in the 
documentation. It must rather be seen as the initial implementation of a 
more extended "AxesSpec" argument, as "LineSpec" already exists and 
makes plot() much more handy than plot2d(). Simply, to me, the priority 
was to transfer the plot2d() log feature to plot(), as a first step. 
Indeed, it was the only feature missing to plot() that somewhat made me 
sticking to plot2d().
plot() can still be improved in many ways, without breaking anything. 
Just about this axesSpec (a report should be posted), here are some 
ideas to go on designing it:

  * allowing to switch the direction of each axis, by using the "-" symbol
  * allowing to set the position, by using a "r", "t", or "c" symbol
    (for Right, Top, Center)
  * allowing to set the grid (for instance with the "_" symbol)
  * allowing to set the legend (for instance as last field, after the
    first @ symbol, since this one is already used in the legacy "leg"
    option)
  * .. for instance using "|" as axis separator (that then could not be
    used in legends)

IMHO, may be it's the right time to announce the deprecation of plot2d() 
in its documentation, to make it an internal in Scilab 6.2 or 6.3.

You seem to fear other plot2d() extra  options. As you, i would not 
regret strf and nax ones, whose names and encoding are very criptic, and 
just impossible to remember. There were likely designed before graphical 
properties were implemented to address them in a detailed way.

About plot() Global properties:
They are dedicated to polylines, not to axes. So adding any axes 
properties to them would break the idea, indeed. Yet, AFAIU still some 
polyline setting can't be tuned through LineSpec nor a Global property, 
like the curve's thickness. It's a pity. We could think about improving 
this.
On the other hand, Global Properties are less useful now than formerly, 
for 2 main reasons:

  * set() is now vectorized: It now allows to set several properties in
    a single call. This is a quite recent feature (added in ~6.0.1).
  * Assigning a given property for a vectors of handles (as a group of
    polylines) has been a lot of improved in 6.0.2

This recent double vectorization makes complex assignements of (scalar 
or non scalar) values to vectors of polylines handles much easier, and 
in a more extensive way than only through  Global properties.

About any semilogx, semilogy, loglog functions:
When in 2D 3 functions can be simply replaced with 3 understandable 
values of a single option in an existing function, that just tells that 
they are completely useless.
Who would tell that in 3D we would have to create 7 separate functions 
to deal with all x/y/z log/normal possible combinations? So why doing it 
in 2D?
And why only for the log status? Then, in the same way, why not creating 
some invXplot(), invYplot(), invXYplot(), to directly plot inverted 
axes, and so, of course, invSemilogX(), etc..?
To me, all this is just meaningless.
Now, if former matlabers wish to still use their prefered former 
functions, of course adding them in an external compatibility toolbox is 
possible, as you did in plotlib.
By the way, similar functions already exist in Scilab, as mtlb_semilogx, 
mtlb_semilogy, mtlb_loglog, in the m2sci module.

We can't on one hand make strong efforts to remove all existing 
duplicates or uselessly split features, and on the other one make strong 
efforts to build new ones as somewhat strange and absurd ones that 
already exist.
At least, if so, personnally i would not go on about any cleaning and 
clarifying task in Scilab.

This is why, to me, the introduced AxesSpec feature is great, clear, 
fully enabled, and already complete for log/lin tuning at calling time.
While i am sorry to still not understanding your point.

Best regards
Samuel


Le 13/03/2020 à 11:18, Stéphane Mottelet a écrit :
> Hi,
>
> I don't approve this commit 
> (https://codereview.scilab.org/#/c/20879/8) which was merged just 
> before the release (I didn't even have the time to give it a -1). It 
> represents a complete breakdown with the spirit of "plot", whose help 
> page says "plot has been rebuild to better handle Matlab syntax. To 
> improve graphical compatibility, Matlab users should use plot (rather 
> than plot2d)". Until now, the behavior of plot was customized by means 
> of "propertyName/value" pairs given after the (x,y) pairs.
>
> With this new logflags syntax, we have an optionnal first argument of 
> "value" type without its "propertyName", moreover this is a "value" of 
> an Axes property. At worse, but it would not have been more coherent, 
> the expected feature could have been implemented as a pair 
> "log_flags",string among other "propertyName/value".
>
> plot() had the merit of being more user friendly that plot2d(). With 
> this commit, it started its convergence towards plot2d(), which is not 
> a reference of user friendliness. One implicit rule is: when we 
> introduce functions with Matlab's functions names and trying to 
> emulate some of its features, then the Scilab function has to respect 
> the subset of the Matlab API it implements and not mix with custom 
> Scilab syntax. There are plenty of such functions in Scilab and this 
> is a pity. We have implemented plot(), mesh(), surf(), light() and 
> instead of breaking plot() to allow logarithmic plots it would have 
> been simpler to emulate the corresponding functions in Matlab, namely, 
> semilogx(), semilogy(), loglog(). So I hope that this commit will be 
> quickly reverted in favor of https://codereview.scilab.org/#/c/21436/, 
> in order to prevent bad habits of average users who could start using 
> the logflags syntax.
>
> S.
>

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