I am interested in finding the final value of the x-axis for this graph.
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I've tried using the Xlim command to obtain the range of values along the x-axis, but it gave me the range of the entire graph ([0 250000]) rather than the final value of the graph, located around ~22000 Hz. Is there a function in MATLAB that can find this value for me?
Assuming your x-values are in the variable 'x' just do:
max(x)
I'm assuming you want to obtain that value from the graph, that is, you don't have access to the variables that originated the graph.
Get the 'XData' and 'YData' of the plotted curve, and then look for the point with greatest x value:
ch = get(gca, 'Children'); %// all children of current axes
ch = findobj(ch, 'type', 'line'); %// keep only line objects
xData = get(ch(1), 'XData'); %// take first line object, if there are more than one
yData = get(ch(1), 'YData');
[resultX, ind] = max(xData); %// resultX is the greatest x value in the graph
resultY = yData(ind); %// resultY is the corresponding y value
Related
I wish to highlight/mark some parts of a array via plot in MATLAB. After some research (like here) I tried to hold the first plot, find the indexes for highlighting and then a new plot, only with those points. However, those points are being drawn but all shifted to the beginning of the axis:
I'm currently trying using this code:
load consumer; % the main array to plot (157628x10 double) - data on column 9
load errors; % a array containing the error indexes (1x5590 double)
x = 1:size(consumer,1)'; % returns a (157628x1 double)
idx = (ismember(x,errors)); % returns a (157628x1 logical)
fig = plot(consumer(:,9));
hold on, plot(consumer(idx,9),'r.');
hold off
Another thing I would like to do was highlighting the whole section of the graph, like a "patch" on the same sections. Any ideas?
The trouble is that you are only providing the y-axis data to the plot function. By default, this means all data is plotted on the 1:numel(y) x locations of your plot, where y is your y-axis data.
You have 2 options...
Also provide x-axis data. You've already got the array x anyway!
figure; hold on;
plot(x, consumer(:,9));
plot(x(idx), consumer(idx,9), 'r.');
Aside: I'm slightly confused why you create idx. If errors is as you describe it (indexes of the array) then you should just be able to use consumer(errors,9).
Make all data which you don't want to appear equal to NaN. Because of the way you're loading your error indices in, this is less quick and easy. Basically you'd copy consumer(:,9) into a new variable, and index all undesirable points to set them equal to NaN.
This method has the benefit of breaking up discontinuous sections too.
y = consumer(:,9); % copy your y data before changes
idx = ~ismember(x, errors); % get the indices you *don't* want to re-plot
y(idx) = NaN; % Set equal to NaN so they aren't plotted
figure; hold on;
plot(x, consumer(:,9));
plot(x, y, 'r'); % Plot all points, NaNs wont show
I have a spectral data (1000 variables on xaxis, and peak intensities as y) and a list of peaks of interest at various specific x locations (a matrix called Peak) which I obtained from a function I made. Here, I would like to draw a line from the maximum value of each peaks to the xaxis - or, eventually, place a vertical arrow above each peaks but I read it is quite troublesome, so just a vertical line is welcome. However, using the following code, I get "Error using line Value must be a vector of numeric type". Any thoughts?
X = spectra;
[Peak,intensity]=PeakDetection(X);
nrow = length(Peak);
Peak2=Peak; % to put inside the real xaxis value
plot(xaxis,X);
hold on
for i = 1 : nbrow
Peak2(:,i) = round(xaxis(:,i)); % to get the real xaxis value and round it
xline = Peak2(:,i);
line('XData',xline,'YData',X,'Color','red','LineWidth',2);
end
hold off
Simple annotation:
Here is a simple way to annotate the peaks:
plot(x,y,x_peak,y_peak+0.1,'v','MarkerFaceColor','r');
where x and y is your data, and x_peak and y_peak is the coordinates of the peaks you want to annotate. The add of 0.1 is just for a better placing of the annotation and should be calibrated for your data.
For example (with some arbitrary data):
x = 1:1000;
y = sin(0.01*x).*cos(0.05*x);
[y_peak,x_peak] = PeakDetection(y); % this is just a sketch based on your code...
plot(x,y,x_peak,y_peak+0.1,'v','MarkerFaceColor','r');
the result:
Line annotation:
This is just a little bit more complicated because we need 4 values for each line. Again, assuming x_peak and y_peak as before:
plot(x,y);
hold on
ax = gca;
ymin = ax.YLim(1);
plot([x_peak;x_peak],[ymin*ones(1,numel(y_peak));y_peak],'r')
% you could write instead:
% line([x_peak;x_peak],[ymin*ones(1,numel(y_peak));y_peak],'Color','r')
% but I prefer the PLOT function.
hold off
and the result:
Arrow annotation:
If you really want those arrows, then you need to first convert the peak location to the normalized figure units. Here how to do that:
plot(x,y);
ylim([-1.5 1.5]) % only for a better look of the arrows
peaks = [x_peak.' y_peak.'];
ax = gca;
% This prat converts the axis unites to the figure normalized unites
% AX is a handle to the figure
% PEAKS is a n-by-2 matrix, where the first column is the x values and the
% second is the y values
pos = ax.Position;
% NORMPEAKS is a matrix in the same size of PEAKS, but with all the values
% converted to normalized units
normpx = pos(3)*((peaks(:,1)-ax.XLim(1))./range(ax.XLim))+ pos(1);
normpy = pos(4)*((peaks(:,2)-ax.YLim(1))./range(ax.YLim))+ pos(2);
normpeaks = [normpx normpy];
for k = 1:size(normpeaks,1)
annotation('arrow',[normpeaks(k,1) normpeaks(k,1)],...
[normpeaks(k,2)+0.1 normpeaks(k,2)],...
'Color','red','LineWidth',2)
end
and the result:
How do I find the actual y-range here:
This is just the example from the docs http://www.mathworks.com/help/matlab/ref/axis.html
x = linspace(-10,10,200);
y = sin(4*x)./exp(.1*x);
plot(x,y)
axis([-10 10 0 inf])
the ymin value is specified as zero and the max left automatic. If I now query the range with
get(gca,'YLim')
I just get [ 0 inf ]. How do i determine the actual plot y range used ( it is about [0 2.5] for this example..)
edit - aside
In case anyone else encounters this - it may be preferable to avoid the issue: make the plot with fully automatic ranging then fix the range as you like so you know exactly what it is, eg.
plot(x,y)
origYrange=ylim
origXrange=xlim
axis([origXrange 0 origYrange(2)])
Although the documentation doesn't tell, it appears that when the first (second) value of ylim is set to -inf (inf) Matlab sets the lower (upper) y-axis limit as the minimum (maximum) of all y values in the plot. The latter can be known by reading the 'YData' property of all 'children' of the axis.
yd = get(get(gca,'children'),'YData'); %// get y data of all plots
if iscell(yd) %// if there's more than one plot yd is a cell array of numeric vectors;
%// otherwise it's a numeric vector
yd = [yd{:}]; %// combine all values into a single numeric vector
end
ydminmax = [min(yd) max(yd)]; %// computed limits
result = ylim;
ind = isinf(result);
result(ind) = ydminmax(ind); %// replace infinite values by computed values
In your example, the result is
result =
0 2.4313
I haven't used MATLAB in a while and I am stuck on a small detail. I would really appreciate it if someone could help me out!
So I am trying to plot a transfer function using a specific function called freqs but I can't figure out how I can label specific points on the graph.
b = [0 0 10.0455]; % Numerator coefficients
a = [(1/139344) (1/183.75) 1]; % Denominator coefficients
w = logspace(-3,5); % Frequency vector
freqs(b,a,w)
grid on
I want to mark values at points x=600 Hz and 7500 Hz with a marker or to be more specific, points (600,20) and (7500,-71), both of which should lie on the curve. For some reason, freqs doesn't let me do that.
freqs is very limited when you want to rely on it plotting the frequency response for you. Basically, you have no control on how to modify the graph on top of what MATLAB generates for you.
Instead, generate the output response in a vector yourself, then plot the magnitude and phase of the output yourself so that you have full control. If you specify an output when calling freqs, you will get the response of the system.
With this, you can find the magnitude of the output by abs and the phase by angle. BTW, (600,20) and (7500,-71) make absolutely no sense unless you're talking about magnitude in dB.... which I will assume is the case for the moment.
As such, we can reproduce the plot that freqs gives by the following. The key is to use semilogx to get a semi-logarithmic graph on the x-axis. On top of this, declare those points that you want to mark on the magnitude, so (600,20) and (7500,-71):
%// Your code:
b = [0 0 10.0455]; % Numerator coefficients
a = [(1/139344) (1/183.75) 1]; % Denominator coefficients
w = logspace(-3,5); % Frequency vector
%// New code
h = freqs(b,a,w); %// Output of freqs
mag = 20*log10(abs(h)); %// Magnitude in dB
pha = (180/pi)*angle(h); %// Phase in degrees
%// Declare points
wpt = [600, 7500];
mpt = [20, -71];
%// Plot the magnitude as well as markers
figure;
subplot(2,1,1);
semilogx(w, mag, wpt, mpt, 'r.');
xlabel('Frequency');
ylabel('Magnitude (dB)');
grid;
%// Plot phase
subplot(2,1,2);
semilogx(w, pha);
xlabel('Frequency');
ylabel('Phase (Degrees)');
grid;
We get this:
If you check what freqs generates for you, you'll see that we get the same thing, but the magnitude is in gain (V/V) instead of dB. If you want it in V/V, then just plot the magnitude without the 20*log10() call. Using your data, the markers I plotted are not on the graph (wpt and mpt), so adjust the points to whatever you see fit.
There are a couple issues before we attempt to answer your question. First, there is no data-point at 600Hz or 7500Hz. These frequencies fall between data-points when graphed using the freqs command. See the image below, with datatips added interactively. I copy-pasted your code to generate this data.
Second, it does not appear that either (600,20) or (7500,-71) lie on the curves, at least with the data as you entered above.
One solution is to use plot a marker on the desired position, and use a "text" object to add a string describing the point. I put together a script using your data, to generate this figure:
The code is as follows:
b = [0 0 10.0455];
a = [(1/139344) (1/183.75) 1];
w = logspace(-3,5);
freqs(b,a,w)
grid on
figureHandle = gcf;
figureChildren = get ( figureHandle , 'children' ); % The children this returns may vary.
axes1Handle = figureChildren(1);
axes2Handle = figureChildren(2);
axes1Children = get(axes1Handle,'children'); % This should be a "line" object.
axes2Children = get(axes2Handle,'children'); % This should be a "line" object.
axes1XData = get(axes1Children,'xdata');
axes1YData = get(axes1Children,'ydata');
axes2XData = get(axes2Children,'xdata');
axes2YData = get(axes2Children,'ydata');
hold(axes1Handle,'on');
plot(axes1Handle,axes1XData(40),axes1YData(40),'m*');
pointString1 = ['(',num2str(axes1XData(40)),',',num2str(axes1YData(40)),')'];
handleText1 = text(axes1XData(40),axes1YData(40),pointString1,'parent',axes1Handle);
hold(axes2Handle,'on');
plot(axes2Handle,axes2XData(40),axes2YData(40),'m*');
pointString2 = ['(',num2str(axes2XData(40)),',',num2str(axes2YData(40)),')'];
handleText2 = text(axes2XData(40),axes2YData(40),pointString2,'parent',axes2Handle);
Hi can somebody help me with the Matlab command here. I've got to determine the highest point in a filled contour I've plotted using matrix data in a file. And then I have to mark the highest point with a red x.
load('0101862_mod.dtm') % loading the dtm file
X = X0101862_mod(1:81,:) % we name X0101862, it is the location where the data X, Y and Z is stored
Y = X0101862_mod(82:162,:)
Z = X0101862_mod (163:243,:)
figure (1)
subplot(2,2,3)
[C,h] = contourf(X,Y,Z,10);
xlabel('x'); ylabel('y'); zlabel('z'); title('X0101862_mod');
view(-73,34); axis equal; colormap summer; colorbar;
i know it involves max command. Kept getting error when i use max.
To plot the red 'X', you have to call first hold on to make sure that the second plotting command won't erase the contour. Then, you use plot(xMax,yMax,'xr') to plot a red 'x' at the x/y coordinates where z is at its maximum.
To find xMax and yMax, you have to use the second output argument of max. MAX returns, as first output, the maximum (e.g. of Z), and as a second output, it returns the number of the element that is maximal. Use that number (the index) to find the elements in X and Y that correspond to the maximum Z-value, i.e. xMax and yMax.