A graphic I can (hardly) do in gnuplot, but not at all in octave

[John W. Eaton]

On  2-Sep-1997, Cautaerts Vincent <address@hidden> wrote:

| Hello,
| 
| I need some help for creating a graphic. Actually, I can not do it
| easily under "gnuplot", but maybe there is a good way to do this kind
| of things. When doing it from gnuplot, I have to manually change
| the data file, which I cannot do everytime under octave !
| 
| In brief, I make some simulations of pulses, and I would like to have
| something like this (let's try ASCII art...)
| 
| y axis
| |
| |    z axis
| |     /          .
| |    /       . .   .  * *
| |   /      .       *.     *
| |  /  .....      *    . ...*............
| | /             *            *
| |/**************               ************
| -----------------------------------------------> x axis
| where *** is supposed to be one line, and .... another.
| 
| If I use "mesh", I have a complete grid: i.e. also lines from some "*" to
| some "."
| 
| Seen from the top of the y axis:
|   WHAT I HAVE          WHAT I'D LIKE         z axis
| +--+--+--+--+--+       -------------         |
| |  |  |  |  |  |                             |
| +--+--+--+--+--+       -------------         +-----> x axis
| |  |  |  |  |  |
| +--+--+--+--+--+       -------------
| ...
| 
| If possible, I would like to have hidden lines, i.e.
| y axis
| |
| |    z axis
| |     /          .
| |    /       . .   .  * *
| |   /      .       *      *
| |  /  .....      *         *............
| | /             *            *
| |/**************               ************
| -----------------------------------------------> x axis
| 
| Then, if somebody
| 1) understands what I mean
| 2) knows how to do it
| please tell me ! 
| 
| When using mesh, I use the command:
| 
| mesh(Memory_z',t',abs(Memory_v)');
| 
| where "Memory_z" is for example a [1 5] vector, with the z coordinates
|                       of my pulses (thus 5 here)
|       "t" is a [1 128] vector with the datas for the x axis
|       "Memory_v" is a [5 128] vector with the datas:
| Memory_v(1,:) contains the first curve
| Memory_v(2,:) the second,...
| 
| I'de like to plot, on a 3d graph, the curves
| Memory_v(1,:) versus t  in the plane z=Memory_z(1) (represented with ** here)
| Memory_v(2,:) versus t  in the plane z=memory_z(2) (represented with .. here)
| ...

I think gnuplot (and Octave) can almost do what you want.  In Octave,
create a matrix that includes the lines you want to plot, like this:

  data = [x1, y1, z1, x2, y2, z2, ..., xn, yn, zn];

where each x1, y1, z1, etc., represents a column of data.  Then set
gnuplot's parametric plotting mode and plot the matrix using gsplot:

  gset parametric
  gsplot data

For example:

  x = (0:0.2:6)';
  n = length (x);
  z = zeros (n, 3*n);
  for i = [1:n-2, n, n-1]
    z(:,3*i-2) = x;
    z(:,3*i-1) = i;
    z(:,3*i) = [sin(x(i:n)); sin(x(1:i-1))];
  endfor
  gset parametric
  gplot data

The problem is that if your data looks like it forms a grid (and this
matrix will), then gnuplot seems to want to draw the mesh lines.  So
far, the only way I've found to turn this feature off involves editing
the generated data file, or by creating the data file for gnpulot
using fprintf.  There may be a more convenient way, but I
haven't found it yet.

jwe