Hi I'm starting to use Octave and need help on how to plot x²+y² = 1.
I know that the figure is a cylinder.
I tried:
x= -10:0.1:10;
y = -10:0.1:10;
t = x²+y²;
but it won't work.
For this particular situation, you can just use the cylinder function.
cylinder([a,b])
will plot a cylinder whose radius at z==0 will be equal to a, and will vary continuously and smoothly until its radius at z==1 reaches b. In you case, you need to set a and b to 1, which is what happens by default when you call cylinder().
Now this will plot the cylinder with only z values in [0,1]. If you want to customize that range, you can just get the output from the function like this:
[xx yy zz]=cylinder([1,1]);
And now you can use this to obtain the plot that you want. For example,
surf(xx,yy,zz.*10);hold on; surf(xx,yy,-zz.*10);
will produce this:
Related
I have three arrays of equal size: x, y, z. I want to plot z over x, y. Problems is, those x and y do not represent a rectangular region, such as what would be in case of using meshgrid function.
I know I can use something like scatter, but that would graphically only give me the points themselves. What I want is the filled, smoothed picture. So as opposed to this created by scatter:
I would like something like this:
Any suggestion how this can be done? I have a feeling the data must be smoothed out somehow via interpolation or something else prior to plotting which itself should be simple.
You can use griddata() to interpolate your x,y data on a regular grid and then you can use imagesc() to plot the result.
Here is a minimal example with a basic circle:
% INPUT
x = cos(0:0.1:2*pi);
y = sin(0:0.1:2*pi);
z = (0:0.1:2*pi);
% Create a regular grid that have the same boundary as your x,y data
[xx,yy] = meshgrid(linspace(-1,1,100),linspace(-1,1,100));
% Grid interpolation
zz = griddata (x, y, z, xx, yy);
% Plot
imagesc(zz)
colormap ([jet(); 1 1 1]); % I add a last [1 1 1] triplet to set the NaN color to white.
Noticed that this will only works if you keep the default interpolation method (which is a linear interpolation). The other method (cubic and nearest) will extend the domain of definition by analytic continuation.
I realized that the best approach would be some slight modification to what obchardon is proposing:
instead of the lines
imagesc(zz)
colormap ([jet(); 1 1 1]);
do this:
surf(xx, yy, zz);
shading interp;
colormap("jet");
This eliminates the problem with the black background. Then all it takes is just to rotate the camera with a mouse so that the 3d surface looked like 2d from above.
I am trying to generate a plot which uses arrows as markers in Gnuplot. These arrows I want to turn in a specific angle which I know. So I have value triples of x1 ... xn, y1...yn, alpha1...alphan. Sorry, I wasn't able to include a pic from my hard drive to illustrate what I want to achieve.
Basically, for every (15th or so) x-y pair, the marker should be an arrow which uses a certain angle.
The measured data is tightly packed so I suppose I will have to define an increment between the markers. The length of the arrow can be the same all over.
I would appreciate your ideas.
Gnuplot has a plot mode with vectors that is what you want
Given that your file has the following format, x y angle and assuming that
your angle is in radians, you have to take into account that
with vectors requires 4 parameters, namely x y dx dy where dx
and dy are the projections of the lenght of the arrow.
this draws only the arrows, if you want a line you have to make
two passes on the data.
you want to draw an arrow for a data point over, say, 10 points.
That said, I'd proceed like this
dx(a) = 0.2*cos(a) # 0.2 is an arbitrary scaling factor
dy(a) = 0.2*sin(a)
# this draws the arrows
plot 'mydata.dat' every 10 using 1:2:(dx(a)):(dy(a)) with vectors
# this draws the line
plot 'mydata.dat'
You may want to use help plot to find the detailed explanation of all the parameters that you can apply to a with vectors plot.
Credits: An article on the gnuplotting site
I need to draw a line between two specific values from a plot in R. That's what I want. If it is possible to draw a line between those two consecutive values which the difference between values is higher than 3. Else, draw it knowing the values from the dataset. Also, I would like to add a number under or above the line. Thanks.
Here the link where you can find the image "ImageR.png"
https://www.dropbox.com/sh/blnr3jvius8f3eh/AACOhqyzZGiDHAOPmyE__873a?dl=0
Something like this should do it. You may have to play with pos and offset in text to get it to look good on your data.
x <- rnorm(20, sd=3)
d <- diff(x)
plot(x)
for (i in which(d>3)) {
lines(c(i,i+1), x[i:(i+1)])
text(i+.5, mean(x[i:(i+1)]), round(d[i],1), pos=2)
}
I am trying to create a figure like the one depicted in the third column of the following image:
Link for the image in case of backup.
Basically I have x and y positions of 200 particles and I have the MSD data for these 200 positions. I'd like MSD to be the value that should determine a color map for the particles in coordinates (x,y). So MSD should be like the height, or the z position corresponding to each particle in (x,y).
I am surprised at my incompetence, because I have been trying to solve this problem for the last couple of days but none of the Google searches gave me any result. The closest thing that I have found is the concept of "self-organizing map" in Matlab and R, but I do not know how to use R and Matlab's toolbox for SOM was utterly useful for my needs.
I tried the following code in Matlab and get the attached plot as a result:
clear all; close all; clc;
x = (dlmread('xdata.dat'))'; % x is 1x200 array
y = (dlmread('ydata.dat'))'; % y is 1x200 array
msd = (dlmread('msd_field.txt'))'; % msd is 1x200 array
[X,Y] = meshgrid(x,y);
Z = meshgrid(msd);
z = [X; Y; Z];
surf(z)
But I think this plot is not useful at all. What I want is a 2D scatter plot of (x,y) depicting particle positions and on top of that color code this scatter plot with the values stored in msd like the plot I showed in the beginning. How can I create this through Matlab, or any other visualization tool? Thank you in advance.
It is not clear whay you want to have. Here a scatter plot using ggplot2.
## some reproducible data
set.seed(1)
dat <- data.frame(
x = round(runif(200,-30,30),2),
y = round(runif(200,-2,30),2),
msd = sample(c(0,2,3),200,rep=T))
## scatter plot where the size/color of points depends in msd
library(ggplot2)
ggplot(dat) +
geom_point(aes(x,y,size=msd,color=msd)) +
theme_bw()
I am able to create a 2-D plot using two parameters in IDL, i.e., star formation rate (y-axis) vs. time (x-axis).
But I would like to include the redshift (another variable) corresponding to each data point, say, as the top x-axis. It didn't work when I tried adding the third variable to PLOT procedure, and I have not been able to find any discussion on how to accomplish this online. Any help is appreciated.
First run PLOT.PRO with the NODATA keyword set and XAXIS=4 and YAXIS=4 to suppress each axis. Then you can use the AXIS.PRO program to define each axis. Then you can use OPLOT.PRO to draw the points of Z vs. X and Z vs. Y, where Z = star formation rate, X = time, and Y = redshift. Look up details on the [XYZ]AXIS keywords to determine which axis to draw at each time. You can even color each axis using the COLOR keyword with the AXIS.PRO program.
The only trick is that you will have to scale the Y data points to the X-axis scale prior to plotting because you will explicitly define the [XYZ]RANGE when calling PLOT.PRO (well you could do the converse and scale it to Y and redefine X, it's your choice). You need to do this scaling because OPLOT.PRO and, say, PLOTS.PRO use the original [XYZ]RANGE defined when calling PLOT.PRO to convert device coordinates to data coordinates.
Does that make sense?
first call PLOT, TIME, SFR with XSTYLE=9 to force exact range and suppress the top x-axis
then use the AXIS procedure to create the top x-axis
be careful with the ticks of that axis, which you want to correspond to a REDSHIFT that you compute from the TIME variable
example with a bottom x-axis in velocity and a top y-axis in frequency:
> plot, vel, spec, xsty=9, xtick_get=xtick, xtit='Velocity (km/s)', ytit='Antenna Temperature (K)'
> axis, !x.crange[0], !y.crange[1], xaxis=1, xtickv=((ref_freq - ref_freq/299792.458*xtick)), xtickformat='(F8.3)', xticks=n_elements(xtick)-1, xrange=(ref_freq - ref_freq/299792.458*minmax(!x.crange)), chars=1.5
You could always set the color to be the third dimension (ie. color or size).