gnuplot-info

[Gnuplot-info] Option reverse and table

[Loïc <xl...@fr...>]

Hello everyone

I have to use table terminal mode to recover the coordinates from a
plotted function with decreasing X.

Example: I want to plot the function f(x)=x^2 between 0 and 10
I want the coordinates from x=10 to x=0

------------------------------------
The commands I wrote:

set table "out" 
set xrange [0:10] reverse
plot x**2
------------------------

Then I edit the file called "out"
but the first lines are:

 0  0  i
 0.10101  0.010203  i
 0.20202  0.0408122  i
 0.30303  0.0918274  i
 0.40404  0.163249  i
 0.505051  0.255076  i
 0.606061  0.367309  i
 0.707071  0.499949  i
 0.808081  0.652995  i
 0.909091  0.826446  i
 1.0101  1.0203  i
..............
Hence, x are in increasing mode, and not decreasing as I wish.

Is it a bug ? If it isn't, how can I release what I want?
Thanks in advance

Best regards

Loïc

Re: [Gnuplot-info] Option reverse and table

[Hans-Bernhard B. <HBB...@t-...>]

Loïc wrote:

> set table "out" 
> set xrange [0:10] reverse
> plot x**2

[...]

> Hence, x are in increasing mode, and not decreasing as I wish.
> 
> Is it a bug ? 

No.  There's no promise of the range reversal affecting sampling order. 
  It affects the relation between coordinates and positions on a graph, 
not the order in which those positions are visited.  That ordering is 
generally unimportant, since you couldn't spot the difference in the 
resulting image anyway.

The table driver makes that a bit mor complicated, of course.  But, like 
with so many problems, parametric mode helps:

gnuplot> set table ; set parametric ; set samples 15
gnuplot> f_x(t) = 10 - t
gnuplot> plot [0:10] f_x(t), f_x(t)**2

#Curve 0 of 1, 15 points
#x y type
  10  100  i
  9.28571  86.2245  i
  8.57143  73.4694  i
  7.85714  61.7347  i
  7.14286  51.0204  i
  6.42857  41.3265  i
  5.71429  32.6531  i
  5  25  i
  4.28571  18.3673  i
  3.57143  12.7551  i
  2.85714  8.16327  i
  2.14286  4.59184  i
  1.42857  2.04082  i
  0.714286  0.510204  i
  0  0  i

Re: [Gnuplot-info] Option reverse and table

[Loïc <xl...@fr...>]

Many thanks, I didn't think at a parametric curve.

Loïc

Le mercredi 23 juillet 2008 à 00:15 +0200, Hans-Bernhard Bröker a
écrit :
> Loïc wrote:
> 
> > set table "out" 
> > set xrange [0:10] reverse
> > plot x**2
> 
> [...]
> 
> > Hence, x are in increasing mode, and not decreasing as I wish.
> > 
> > Is it a bug ? 
> 
> No.  There's no promise of the range reversal affecting sampling order. 
>   It affects the relation between coordinates and positions on a graph, 
> not the order in which those positions are visited.  That ordering is 
> generally unimportant, since you couldn't spot the difference in the 
> resulting image anyway.
> 
> The table driver makes that a bit mor complicated, of course.  But, like 
> with so many problems, parametric mode helps:
> 
> gnuplot> set table ; set parametric ; set samples 15
> gnuplot> f_x(t) = 10 - t
> gnuplot> plot [0:10] f_x(t), f_x(t)**2
> 
> #Curve 0 of 1, 15 points
> #x y type
>   10  100  i
>   9.28571  86.2245  i
>   8.57143  73.4694  i
>   7.85714  61.7347  i
>   7.14286  51.0204  i
>   6.42857  41.3265  i
>   5.71429  32.6531  i
>   5  25  i
>   4.28571  18.3673  i
>   3.57143  12.7551  i
>   2.85714  8.16327  i
>   2.14286  4.59184  i
>   1.42857  2.04082  i
>   0.714286  0.510204  i
>   0  0  i
> 
>