Re: plot matrix?

[Ethan M. <merritt@u.washington.edu>]

On Saturday 21 November 2009, Philipp K. Janert wrote:
> 
> I am not sure how the "matrix" keyword works
> (that is: is supposed to work) when used together
> with the plot (not splot) command.

I share your confusion.

> Can you help me to enumerate the legal uses?
> 
> For splot, there seem to be two legal ways to use
> matrix:
> 
> 	splot "file" matrix 
> and
> 	splot "file" matrix u ($1):($2):3

In addition, ascii matrices and binary matrices are treated
very differently according to the docs.

> The first assumes the values in the file to be z-values
> on a regular grid.
>
> The second assumes that the z-values are in "column"
> 3, and allows me to fix the x- and y-coordinates through
> the "columns" 1 and 2.
> 
> Is it legal to do either:
> 
> 	splot "file" matrix u 1
> or
> 	splot "file" matrix 1:2
> 
> And if so, what do either of them do?
> 
> For plot (not splot), I am completely confused. Does
> it even make sense to have the notion of a "matrix"
> format for plot? The "matrix" keyword seems to suggest
> that the data is on a regular, 2-dim grid. This notion 
> does not seem to have any meaning for plot.

It is clearly useful to have such a capability.
I use it to make heat maps, for instance.
See heatmaps.dem
But whether I use it in the way orginally intended is another
question :-)


Another bizarre property is that the following command can be
used to plot the values in a row of data rather than a column
of data, which is otherwise "impossible" in a normal gnuplot command:

     plot 'rowdata' matrix using 1:0

I suspect this was totally unintended.  At one point I tried
to figure out if this was generalizable, but I got too confused
and gave it up.