gnuplot documentation

98 gnuplot 4.3 70 SET-SHOW
set dgrid3d {} {,{} {,}}
unset dgrid3d
show dgrid3d
By default dgrid3d is disabled. When enabled, 3D data read from a file are always treated as a scattered
data set. A grid with dimensions derived from a bounding box of the scattered data and size as specified
by the row/col size parameters is created for plotting and contouring. The grid is equally spaced in x
(rows) and in y (columns); the z values are computed as weighted averages of the scattered points’ z
values.
The third parameter, norm, controls the weighting: Each data point is weighted inversely by its distance
from the grid point raised to the norm power. (Actually, the weights are given by the inverse of dx^norm
+ dy^norm, where dx and dy are the components of the separation of the grid point from each data point.
For some norms that are powers of two, specifically 4, 8, and 16, the computation is optimized by using
the Euclidean distance in the weight calculation, (dx^2+dy^2)^norm/2. However, any non-negative
integer can be used.)
The closer the data point is to a grid point, the more effect it has on that grid point and the larger the
value of norm the less effect more distant data points have on that grid point.
The dgrid3d option is a simple low pass filter that converts scattered data to a grid data set. More
sophisticated approaches to this problem exist and should be used to preprocess the data outside gnuplot
if this simple solution is found inadequate.
(The z values are found by weighting all data points, not by interpolating between nearby data points;
also edge effects may produce unexpected and/or undesired results. In some cases, small norm values
produce a grid point reflecting the average of distant data points rather than a local average, while
large values of norm may produce "steps" with several grid points having the same value as the closest
data point, rather than making a smooth transition between adjacent data points. Some areas of a grid
may be filled by extrapolation, to an arbitrary boundary condition. The variables are not normalized;
consequently the units used for x and y will affect the relative weights of points in the x and y directions.)
Examples:
set dgrid3d 10,10,1
set dgrid3d ,,4
# defaults
The first specifies that a grid of size 10 by 10 is to be constructed using a norm value of 1 in the weight
computation. The second only modifies the norm, changing it to 4. See also
scatter.dem:
dgrid3d demo.
70.17 Dummy
The set dummy command changes the default dummy variable names.
Syntax:
set dummy {} {,}
show dummy
By default, gnuplot assumes that the independent, or "dummy", variable for the plot command is
"t" if in parametric or polar mode, or "x" otherwise. Similarly the independent variables for the splot
command are "u" and "v" in parametric mode (splot cannot be used in polar mode), or "x" and "y"
otherwise.
It may be more convenient to call a dummy variable by a more physically meaningful or conventional
name. For example, when plotting time functions:
set dummy t
plot sin(t), cos(t)
At least one dummy variable must be set on the command; set dummy by itself will generate an error
message.
Examples: