I would like to add arrows to a plot of a line in Matlab to illustrate flow. The arrows would ideally be on the line pointing in the direction of the line. Is this possible?
In order to draw an arrow in Matlab, use the file exchange free package called arrow.m
Another way is to use great submission on FileExchange - ARROW.M
See also other related questions on SO:
How do I display an arrow positioned
at a specific angle in MATLAB?
How to add a pointer to a 3-D plot
in MATLAB?
The quiver function should be able to do what you want. However, you'll have to compute the direction of the arrow yourself.
Something along the lines of this is ugly but should get you started (but you probably want to normalize the direction vector to get a nicer graph)
plot(x,y)
hold on
quiver(x(1:end-1), y(1:end-1), ones(len(x)-1,1), y(2:end) - y(1:end-1))
If I understood correctly, you are trying to view a vector field?
If that's the case, here is a working example:
%# function: f(x,y)=x^3-2y^2-3x over x=[-2,2], y=[-1,1]
[X Y] = meshgrid(-2:.1:2, -1:.1:1);
Z = X.^3 -2*Y.^2 -3*X;
%# gradient of f
[dX dY] = gradient(Z, .1, .1);
%# plot the vector field and contour levels
figure, hold on
quiver(X, Y, dX, dY)
contour(X, Y, Z, 10)
axis equal, axis([-2 2 -1 1])
hold off
%# plot surface
figure, surfc(X, Y, Z)
view(3)
You can add an arrow to a figure by using the function annotation.
Note that the parent of the object is not the axes, but the figure window iteslf (meaning that when you zoom in/out, the arrow keeps on the same location in the figure window).
Related
Potentially easy matlab question here, but I've searched and can't sort out how to do this.
I've got a variables, which plot like this:
I simple want the x axis to be the y axis and vice versa. How do I swap them?
Thank you in advance for your help!!
The standard way would be to swap the arguments passed to plot:
plot(ydata, xdata) %// instead of plot(xdata, ydata)
Failing that, you can change the view to rotate the axes:
view([90 -90]) %// instead of normal view, which is view([0 90])
I just have a brief question regarding MatLab.
Say that we have the equation:
r^2 = 2 sin(5t)
I know that I can fill a polar plot by writing, say:
t = linspace(0,2*pi,200);
r = sqrt(abs(2*sin(5*t)));
x = r.*cos(t);
y = r.*sin(t);
fill(x,y,'k')
But say I use the ezpolar instead by giving the equation above a function handle and then typing:
ezpolar(function handle)
Is there any way I can then fill this polar plot? Or do I have to use the procedure outlined above?
Any tips/help will be greatly appreciated!
You can use ezpolar, then modify the resulting figure. If you look at the returned handle from ezpolar, you'll see it is the line itself drawn in the axis. The points from that line object can be extracted, then used to lay a new polygon on top of the same axis. The benefit is, you get to keep all the nice polar lables.
h=ezpolar('sqrt(abs(2*sin(5*t)))')
hold on;
fill(get(h, 'XData'), get(h, 'YData'), 'k');
I have a script to create scatter plots (using gscatter) based on x-y data (discrete data points, not continuous) produced by another script. Since these data points are actually the locations of certain objects in a circular space, adding polar grid lines will make the plots more meaningful.
Does anyone know how to show polar grid lines on a Cartesian scatter plot, or am I better off using polar plots?
I once made this script for drawing a polar coordinate system on top of a regular plot. Perhaps it can be useful for you. It is based on this script but simplified to only draw the coordinate system and no data. If this wasn't what you were looking for, check out the linked script, perhaps it can help as well.
Be sure to tweak the radius as needed! I usually disable the axis but it's up to you to fix that if you need another look :)
R=6000; %radius
S=10; %num circ.lines
N=10; %num ang.lines
sect_width=2*pi/N;
offset_angle=0:sect_width:2*pi-sect_width;
%------------------
r=linspace(0,R,S+1);
w=0:.01:2*pi;
clf %remove if needed
hold on
axis equal
for n=2:length(r)
plot(real(r(n)*exp(j*w)),imag(r(n)*exp(j*w)),'k--')
end
for n=1:length(offset_angle)
plot(real([0 R]*exp(j*offset_angle(n))),imag([0 R]*exp(j*offset_angle(n))),'k-')
end
%------------------
You can always use the pol2cart function to generate the polar grid lines.
For example:
function DrawGridLines
x = randn(10);
y = randn(10);
figure;scatter(x(:),y(:));
hold on ;
for angle = 0:20:(360-20)
[x1,y1] = pol2cart( angle / 180 * pi , [0 2]);
plot(x1,y1,'r')
end
for rho = 0:0.1:2
[x1,y1] = pol2cart( 0:0.01:2*pi , rho);
plot(x1,y1,'b')
end
axis equal
end
Hi can any one give me a simple example of how to use the isosurface function in MATLAB.
The example given if you type help isosurface is quite confusing. Searching on google did not help as no one gives simple examples anywhere. All of them use predefined functions like
flow.
For starters, suppose i have points (x,y,z) where z=0 and at each point I define a constant
function f(x,y,z)=6. So if I use the isosurface function on the isovalue 6 I would like MATLAB to give me a 3d plot with the XY plane highlighted in some colour, say green.
I don't quite understand your example, but here's how you use isosurface to draw a sphere:
%# create coordinates
[xx,yy,zz] = meshgrid(-15:15,-15:15,-15:15);
%# calculate distance from center of the cube
rr = sqrt(xx.^2 + yy.^2 + zz.^2);
%# create the isosurface by thresholding at a iso-value of 10
isosurface(xx,yy,zz,rr,10);
%# make sure it will look like a sphere
axis equal
The example you gave is very uninteresting, in fact maybe even problematic.
By collapsing all points to z=0, you no longer can/need to use ISOSURFACE, and CONTOUR should be called instead. Even then, a constant function f(X,Y)=6 won't show anything either...
Since #Jonas already showed how to use ISOSURFACE, here is an example for the CONTOUR function:
%# create a function to apply to all X/Y coordinates
[X,Y] = meshgrid(-2:0.1:2,-1:0.1:1);
f = #(X,Y) X.^3 -2*Y.^2 -3*X;
%# plot the function surface
subplot(121), surfc(X,Y,f(X,Y))
axis equal, daspect([1 1 3])
%# plot the iso-contour corresponding to where f=-1
subplot(122), contour(X,Y,f(X,Y),[-1 -1]),
axis square, title('Contour where f(X,Y)=-1')
I'm using polar plots (POLAR(THETA,RHO)) in MATLAB.
Is there an easy way to fix the range for the radial axis to say, 1.5?
I'm looking for something analogous to the xlim, ylim commands for cartesian axes. Haven't found anything in the docs yet.
this worked for me... i wanted the radius range to go to 30, so i first plotted this
polar(0,30,'-k')
hold on
and then plotted what i was actually interested in. this first plotted point is hidden behind the grid marks. just make sure to include
hold off
after your final plotting command.
Here's how I was able to do it.
The MATLAB polar plot (if you look at the Handle Graphics options available) does not have anything like xlim or ylim. However, I realized that the first thing plotted sets the range, so I was able to plot a function with radius range [-.5 .5] on a [-1 1] plot as follows:
theta = linspace(0,2*pi,100);
r = sin(2*theta) .* cos(2*theta);
r_max = 1;
h_fake = polar(theta,r_max*ones(size(theta)));
hold on;
h = polar(theta, r);
set(h_fake, 'Visible', 'Off');
That doesn't look very good and hopefully there's a better way to do it, but it works.
Simple solution is to make a fake graph and set its color to white.
fake=100;
polar(0,fake,'w');
hold on;
real=10;
polar(0,real,'w');
In case anyone else comes across this, here's the solution:
As Scottie T and gnovice pointed out, Matlab basically uses the polar function as an interface for standard plots, but with alot of formatting behind the scenes to make it look polar. Look at the values of the XLim and YLim properties of a polar plot and you'll notice that they are literally the x and y limits of your plot in Cartesian coordinates. So, to set a radius limit, use xlim and ylim, or axis, and be smart about the values you set:
rlim = 10;
axis([-1 1 -1 1]*rlim);
...that's all there is to it. Happy Matlabbing :)