I have created an example scatter plot with five points in MATLAB as follows:
x = linspace(0,pi,5);
y = cos(x);
scatter(x,y);
In my case, the y-value of each point shall be in a predefined range defined as follows:
y_limits = {[0.9 1.1], [0.6 0.8], [-0.1 0.1], [-0.8 -0.6], [-1.1 -0.9]};
So for example, the y value of point 1 at x = 0 shall be in the range [0.9 1.1].
I would somehow like to draw five vertical boundaries nicely in the same plot perhaps by means of
five vertical lines with endpoints at the respective two limits
five filled vertical areas between the respective two limits
something else that may be more appropriate
I would like to get some suggestions or sample code of people who are more experienced than me in such kind of graphical representations.
You can do this in one line by using the errorbar function
% Your example variables
x = linspace(0,pi,5)';
y = cos(x);
y_limits = [0.9, 1.1; 0.6, 0.8; -0.1, 0.1; -0.8, -0.6; -1.1, -0.9];
% Plot
errorbar(x, y, y - y_limits(:,1), y_limits(:,2) - y, 'x');
% Format: (x, y, negative error, positive error, point style)
Result:
Edit, you can set the line properties of the plot as you call errorbar. For example, you could use larger, blue circle markers with thicker, red error bars
using:
errorbar(x, y, y - y_limits(:,1), y_limits(:,2) - y, 'o', 'MarkerSize', 2, 'MarkerFaceColor', 'b', 'MarkerEdgeColor', 'b', 'Color', 'r', 'LineWidth', 1);
Note for these images I'm using grid on to add the grid. Second result:
Creating a lines is done with the line command.
for i = 1:length(x)
line([x(i) x(i)], [y_limits{i}]);
end
Filled areas can be done with patch or fill. Some reordering of the limits is necessary so that the order given follows a path around the area to be filled. One nice trick is to use the alpha command on those filled areas to create transparency.
hold on
y_corners = reshape([y_limits{:}], 2, length(x)).'; %make an array
y_corners = [y_corners(:,1); flipud(y_corners(:,2))]; %corners follow a path around the shape
fill([x fliplr(x)], y_corners, 'blue');
alpha(0.5);
Related
I need to shade a vertical strip area in a MATLAB plot between to vertical lines.
I need to shade the part covered enclosed by the BLACK Curve, RED, BLUE & GREEN Lines.
I have tried the example from Here
If the data for the plot is required, please let me know i will upload.
I think this is what you are looking for:
% some arbitrary data
x = -10:0.1:10;
y = abs(x).^0.5;
xleft = 0.5;
xright = 4;
fillStart = find(x>=0.5,1);
fillEnd = find(x>=4,1);
top = 2.5;
% plotting the lines
plot(x,y,'k',...
x,ones(1,length(x))*top,'r',...
ones(1,length(y)).*xleft,y,'g',...
ones(1,length(y)).*xright,y,'b')
hold on
% filling the area
area(x(fillStart:fillEnd),y(fillStart:fillEnd),top, ...
'EdgeColor', 'none', 'FaceColor', [0.5 0.5 0.5],'ShowBaseLine','off')
hold off
Which create this:
While not exactly what you are after, (you need the equations for your respective lines) something like this should work
x = -5:0.1:5;
y = sqrt(abs(x));
figure
hold on
fill([2, 4, 4, 2], [0, 0, 2, 2], 'g')
plot(x,y)
From the fill documentation
fill(X,Y,C) fills the 2-D polygon defined by vectors X and Y
with the color specified by C. The vertices of the polygon
are specified by pairs of components of X and Y. If necessary,
the polygon is closed by connecting the last vertex to the first.
I want to visualize the peaks of a function, and I want to have markers for it appear above the line they are associated with.
I fabricated a minimum example where I already have the peaks, the question is just how to visualize the markers correctly:
y = [0.1 0.3 10.0 1.0 0.5 0.1 24.0 0.6 0.1 0.2]
x = (1:length(y))
plot(x,y);
hold on;
peaks = [3 7];
plot(x(peaks), y(peaks), 'v', 'MarkerSize', 24);
print('-dpng', 'example.png', '-S640,480');
So, as a result, the markers appear centered on the line like this:
The result that I want could be achieved by carefully tuning a parameter OFFSET like this:
plot(x(peaks), y(peaks)+OFFSET, 'v', 'MarkerSize', 24);
As shown in the following figure, for this exact example OFFSET=2.56 works for the exported png, but with the interactive plot and exporting vector graphics, it's wrong again.
Can anyone recommend a way to get this result without having to manually doing trial/error?
Currently I am using Octave with gnuplot to export to latex+tikz, and it would be good if the solution would work there.
In my actual (more complicated) use case I am plotting multiple lines after each other into the same figure, and the y limits change, so the offsets can not just be calculated easily, as the markersize doesn't change with the y limits.
Edit: Additionally I am using a semilogx plot, so drawing lines inside the diagram in the x/y-Axis scales would look distorted.
One way to do this is with annotations, but there are some drawbacks (see below).
Annotations enable you to place various graphic objects into your figure. One very annoying thing about them is that they work in so-called normalized coordinates,
which span the whole figure window (not just the plot area) and go from [0,0] to [1,1], forcing you to convert to these coordinates first. I wrote a simple function to do this, provided your plot scale is linear (if you want logarithmic, you will have to modify this function):
## Convert from data coordinates to normalized figure coordinates.
function [xf yf] = figcoords(xa, ya)
axp = get(gca, "position");
lf = axp(1);
bf = axp(2);
rf = lf + axp(3);
tf = bf + axp(4);
xl = xlim();
yl = ylim();
la = xl(1);
ra = xl(2);
ba = yl(1);
ta = yl(2);
xf = lf + (xa-la).*(rf-lf)./(ra-la);
yf = bf + (ya-ba).*(tf-bf)./(ta-ba);
endfunction
With this out of your way, you can proceed to annotating the plot using the annotation function:
y = [0.1 0.3 10.0 1.0 0.5 0.1 24.0 0.6 0.1 0.2];
x = (1:length(y));
peaks = [3 7];
## Plot the data as you would normally
plot(x,y);
## Plot peak markers (no `hold on` needed)
[xp yp] = figcoords(peaks, y(peaks)); # Transform to figure coordinates
for coords = [xp; yp]
xpi = coords(1);
ypi = coords(2);
annotation("arrow", [xpi xpi], [ypi+eps ypi]);
endfor
Plot with annotated peaks
Here, we actually draw little arrows pointing from top onto the peaks.
As their height is very small, we only see the arrowheads.
The arguments to the annotation function are the x and y coordinates
of the endpoints of the arrow. Note that we added a small number (eps)
to the y-value of the starting point to make the arrow point downward.
If you want, you can tweak the appearance of the markers to make them more visually appealing:
y = [0.1 0.3 10.0 1.0 0.5 0.1 24.0 0.6 0.1 0.2];
x = (1:length(y));
peaks = [3 7];
coloridx = get(gca, "ColorOrderIndex")
peakcolor = get(gca, "ColorOrder")(coloridx,:); # Save current plot colour
plot(x,y);
## Plot peak markers
[xp yp] = figcoords(peaks, y(peaks));
for coords = [xp; yp]
xpi = coords(1);
ypi = coords(2);
annotation("arrow", [xpi xpi], [ypi+eps ypi], "headstyle", "plain",...
"color", peakcolor);
endfor
Plot with annotated peaks in the same color
Drawbacks
While this approach works fine regardless of the size of the markers or your plot, there are some drawbacks:
First, the annotations are fixed relative to the figure window, not the plot.
This is fine when you display the plot for the first time, but once you zoom
or pan, the alignment is lost: The markes stay in place while the plot moves.
If you don't need an interactive plot (eg, you just want to export it to image),
just be sure to set the plot limits before adding the annotations and you should
be fine.
Second, this method is very slow compared to plotting the points using the
plot function. On my computer, for example, when drawing a simple example with
seven annotated peaks, it takes about a second before the markers appear.
Plotting a signal with thousands of peaks is near impossible.
Concerning the Matlab part, you could draw the peak markers yourself. Somewhere along these lines (extending your example):
y = [0.1 0.3 10.0 1.0 0.5 0.1 24.0 0.6 0.1 0.2]
x = (1:length(y))
figure, plot(x,y);
leglengthx=0.2;
leglengthy=0.5;
hold on;
peaks = [3 7];
peaks_max=[10 24];
for ii=1:2
line([peaks(ii) peaks(ii)+leglengthx],[peaks_max(ii) peaks_max(ii)+leglengthy]);
line([peaks(ii) peaks(ii)-leglengthx],[peaks_max(ii) peaks_max(ii)+leglengthy]);
line([peaks(ii)-leglengthx peaks(ii)+leglengthx],[peaks_max(ii)+leglengthy peaks_max(ii)+leglengthy]);
end
plot(x(peaks), y(peaks), 'v', 'MarkerSize', 24);
I have added the maxima of the peaks, which should not be an issue to automatically extract and two variables that control the triangle size of the marker. And then its just drawing three lines for every peak.
I don't know how this will translate to Octave.
What about drawing the little triangles?
y = [0.1 0.3 10.0 1.0 0.5 0.1 24.0 0.6 0.1 0.2];
x = (1:length(y));
peaks = [3 7];
plot(x,y);
hold on; line([peaks(1) peaks(1)+0.2], [y(x==peaks(1)) y(x==peaks(1))+1], 'color','b')
hold on; line([peaks(1) peaks(1)-0.2], [y(x==peaks(1)) y(x==peaks(1))+1], 'color','b')
hold on; line([peaks(1)+0.2 peaks(1)-0.2], [y(x==peaks(1))+1 y(x==peaks(1))+1], 'color','b')
hold on; line([peaks(2) peaks(2)+0.2], [y(x==peaks(2)) y(x==peaks(2))+1], 'color','b')
hold on; line([peaks(2) peaks(2)-0.2], [y(x==peaks(2)) y(x==peaks(2))+1], 'color','b')
hold on; line([peaks(2)+0.2 peaks(2)-0.2], [y(x==peaks(2))+1 y(x==peaks(2))+1], 'color','b')
There can be a problem if the y-values of the peaks exists in other locations on the vector. If so, you can specify first or other matching specs for the find function.
So I am encountering a couple errors and am not sure where they're coming from. I won't post the whole code, but I will do my best to explain (fear I will be accused of plagiarism).
The assignment is to create a window with two plots: a surface plot and a contour plot. The surface plot represents elevation of a portion of the map represented by the contour plot. The portion is indicated by a blue box on the contour plot. I've successfully plotted the surface and contour plots and have identified the first area with a blue box. However, now I need to implement a menu system wherein the user enters 1, 2, 3, or 4 to move the box north, south, east or west.
Here is how I instantiated the plots:
fig = figure(1);
[xGrid, yGrid] = meshgrid(xMeters(xStart:xEnd), yMeters(yStart:yEnd));
%surface plot
elevationBox = ELEV(xStart:xEnd, yStart:yEnd);
surface = subplot(2, 1, 1);
surf(xGrid, yGrid, elevationBox);
axis([0 max(xGrid(:)) 0 max(yGrid(:)) min(elevationBox(:)) max(elevationBox(:))]);
axis tight;
%contour plot
elevation = ELEV;
[xMap, yMap] = meshgrid(xMeters(1:335), yMeters(1:230));
map = subplot(2, 1, 2); contour(xMap, yMap, elevation);
axis([0 max(xMeters(:)) 0 max(yMeters(:))]);
axis fill;
set(fig, 'Position', [500 100 600 700]);
right = line(xRight, xLeft);
left = line(xLeft, yLeft);
top = line(xTop, yTop);
bottom = line(xBottom, yBottom);
So all that works fine. Obviously I didn't include the parts where I defined the data and everything. After this comes a switch statement that changes the values of xLeft, yLeft, etc as well as xStart, xEnd etc.
Here is my attempt to update the plots:
[xGrid, yGrid] = meshgrid(xMeters(xStart:xEnd), yMeters(yStart:yEnd));
elevationBox = ELEV(xStart:xEnd, yStart:yEnd);
subplot(2, 1, 1)
set(surface, 'XData', xGrid, 'YData', yGrid, 'ZData', elevationBox);
drawnow;
I can choose an option and there is no error, but the plot doesn't update and when I quit the program I get this error:
Error using matlab.graphics.axis.Axes/set
There is no XData property on the Axes class.
Error in A9 (line 129)
set(surface, 'XData', xGrid);
The setting is inside the while loop but outside the switch statement. I also had a few lines using set on the line objects but those weren't working either so I thought I'd focus here first. I'm figuring whatever I'm doing wrong applies to both object types but if not let me know.
Thanks!
Rather than grab a handle to the axis (which you call surface), you want the data object. So grab a handle at surf_h = surf(...);.
A little example:
% Generate a random surface grid
n = 10;
[x, y] = meshgrid(1:n, 1:n);
z = rand(n);
% Plot
fig_h = figure(1);
axis_h = subplot(2, 1, 1);
surf_h = surf(x,y,z);
% Modify XData
set(surf_h, 'XData', -x);
drawnow;
I would like create a Matlab figure with a double X axis (m/s and km/h) with the same plot.
I have found plotyy and - in Matlab reposity - plotyyy, but I am looking for:
A double X axis.
Together below the plot.
My code is very simple:
stem(M(:, 1) .* 3.6, M(:, 3));
grid on
xlabel('Speed (km/h)');
ylabel('Samples');
M(:, 1) is the speed (in m/s), and M(:, 3) is the data.
I would like only a second line, in the bottom, with the speeds in m/s.
You can do something like the following. In comparison to the solution of #Benoit_11 I do use the normal Matlab labels and refer to both axes with handles so the assignments are explicit.
The following code creates an empty x-axis b with the units m/s with a negligible height. After this, the actual plot is drawn in a second axes a located a bit above the other axes and with units km/h. To plot on a specific axes, insert the axes-handle as the first argument of stem. The conversion from m/s to km/h is directly written in the call to stem. Finally, it's needed to set the xlim-property of the both axes to the same values.
% experimental data
M(:,1) = [ 0, 1, 2, 3, 4, 5];
M(:,3) = [12, 10, 15, 12, 11, 13];
% get bounds
xmaxa = max(M(:,1))*3.6; % km/h
xmaxb = max(M(:,1)); % m/s
figure;
% axis for m/s
b=axes('Position',[.1 .1 .8 1e-12]);
set(b,'Units','normalized');
set(b,'Color','none');
% axis for km/h with stem-plot
a=axes('Position',[.1 .2 .8 .7]);
set(a,'Units','normalized');
stem(a,M(:,1).*3.6, M(:,3));
% set limits and labels
set(a,'xlim',[0 xmaxa]);
set(b,'xlim',[0 xmaxb]);
xlabel(a,'Speed (km/h)')
xlabel(b,'Speed (m/s)')
ylabel(a,'Samples');
title(a,'Double x-axis plot');
As a very simple alternative you could also create a 2nd axis (transparent) and put it below the first one so that you only see the x axis.
Example:
clear
clc
close all
x = 1:10;
x2 = x/3.6;
y = rand(size(x));
hP1 = plot(x,y);
a1Pos = get(gca,'Position');
%// Place axis 2 below the 1st.
ax2 = axes('Position',[a1Pos(1) a1Pos(2)-.05 a1Pos(3) a1Pos(4)],'Color','none','YTick',[],'YTickLabel',[]);
%// Adjust limits
xlim([min(x2(:)) max(x2(:))])
text(2.85,0 ,'m/s','FontSize',14,'Color','r')
text(2.85,.05 ,'km/h','FontSize',14,'Color','r')
Output:
Then you can manually add the x labels for each unit, in different color for example.
The best way i can think to do it is to use 2 plots, for example, you can split the plot into a large and small section by doing something like this:
subplot(100, 1, 1:99) // plot your graph as you normally would
plot(...
subplot(100, 1, 100) // Plot a really small plot to get the axis
plot(...)
b = axis()
axis([b(1:2), 0, 0]) // set the y axis to really small
This is untested, you might need to fiddle around a little but it should hopefully put you on the right track.
I have the graph below I need to create two different x-axis. The unique part of this problem is where the min and max values need to be located. The range for is 0-100 for both, however the 100% value on the second x-axis needs to be where the 50% value is on the first. See the picture for clarification. The red is what I need to add using MATLAB.
I did a lot of looking and while it's very simple to put two different axis on one graph, I couldn't find a solution for this particular problem. I'd like this to be done in the code and not plot tools.
How about this
% dummy data
y = 1:80;
x1 = 100*sin( 4*pi*y/80 ).^2 ;
x2 = 100*cos( 5*pi*y/80).^2;
Plot the first line
figure;
line( x1, y, 'Color', 'b', 'LineWidth', 2 );
Get position and size of first plot
haxes1 = gca;
haxes1_pos = get(haxes1,'Position');
set the 100% of second plot to 50% of first ("tweaking" the width of the axis)
haxes1_pos(3) = haxes1_pos(3)/2;
haxes2 = axes('Position',haxes1_pos,'XAxisLocation','top','Color','none','XColor','r');
Plot the second line
line( x2, y, 'Color', 'k', 'LineWidth',2,'Parent',haxes2);
And this is what you get