Re: rgbplot composite fails with gnuplot

[Ben Abbott]

> On Dec 16, 2014, at 8:26 AM, Juan Pablo Carbajal <address@hidden> wrote:
> 
> Tested in 4.1.0+
> repo id 19402:5cd83b466a3e
> 
> octave-cli:1> rgbplot(jet(16),'composite')
> 
> multiplot> plot "-" binary array=16x2 scan=yx origin=(1,1) dx=1 dy=0
> using 1 title "" with image; ;
>                                                                  ^
>           line 0: Sample period must be positive. Try `flip` for
> changing direction
> 
> 
> Can anybody reproduce?
> 
> Do we report bugs that involve gnuplot?
> 

I get the same result using gnuplot 4.6 patchlevel 6.

The error is indicating that dy must be greater than 0.  The m-code which 
produces this gnuplot command is in plot/utils/private/__go_draw_axes__.m at 
lines 554-547.

        titlespec{data_idx} = "title \"\"";
        usingclause{data_idx} = sprintf ("binary array=%dx%d scan=yx 
origin=(%.15g,%.15g) dx=%.15g dy=%.15g using %s",
            x_dim, y_dim, x_origin, y_origin, dx, dy, format);
        withclause{data_idx} = sprintf ("with %s;", imagetype);

The image intended looks a similar to a colorbar, so I expect the problem is on 
Octave's end.

Ben