Legend and LineStyle with Plotyy

[David Bateman]

Sorry for the delay in responding. Issues with plotyy were one of the 
things I wanted to address, before a 3.2.0 release of Octave, and so I 
just stuck your mail on my todo pile. However, I now suspect that your 
problems are harder to address than I'd thought.

Firstly, I propose the simpler example code

x = 0:0.1:2*pi;
y1 = sin (x);
y2 = exp (x - 1);
[ax, h1, h2] = plotyy (x, y1, x - 1, y2, @plot, @semilogy);
set(h1,'LineStyle','-') 
set(h2,'LineStyle','--')
legend([h1, h2], 'y1', 'y2')

to demonstrate the issues. The linestyle issue is in fact a limitation 
of gnuplot and there is not much we can do about it at this point. See 
the comment in __go_draw_axes__.m that states

    ## FIXME -- linetype is currently broken, since it disables the
    ## gnuplot default dashed and solid linestyles with the only
    ## benefit of being able to specify '--' and get a single sized
    ## dashed line of identical dash pattern for all called this way.
    ## All dash patterns are a subset of "with lines" and none of the
    ## lt specifications will correctly propagate into the x11 terminal
    ## or the print command.   Therefore, it is currently disabled in
    ## order to allow print (..., "-dashed") etc. to work correctly.

    ##    if (! isempty (lt))
    ##      fprintf (plot_stream, " linetype %s", lt);
    ##      found_style = true;
    ##    endif

so as the comment states the gnuplot terminal does not respect the 
dashed linestyles, and the code to do it (ie 4 lines) is commented out. 
You can still be dashed lines in the printed plots for your publications 
with the "-dashed" option to the print command.

As for the legend, there is an incompatibility in how Octave and Matlab 
treat legends.. In Octave a legend is assoicated with an axis, whereas 
in Matlab a legend is a new axis object with the keys printed. The 
Octave way of doing it allows easy interfacing with the gnuplot legend 
code. The downside of Octave's choice is that you'd need a legend that 
is different for each of the axes of the plotyy command. In Octave 3.0.2 
you might try something like

x = 0:0.1:2*pi;
y1 = sin (x);
y2 = exp (x - 1);
[ax, h1, h2] = plotyy (x, y1, x - 1, y2, @plot, @semilogy);
axes(ax(1))
legend ('y1')
axes(ax(2))
legend('y2','location','southeast')

Regards
David

-- 
David Bateman                                David.Bateman at motorola.com
Motorola Labs - Paris                        +33 1 69 35 48 04 (Ph) 
Parc Les Algorithmes, Commune de St Aubin    +33 6 72 01 06 33 (Mob) 
91193 Gif-Sur-Yvette FRANCE                  +33 1 69 35 77 01 (Fax) 

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