I have a graph like this and I want to determine the number of peaks. Since it's a wave function the whole graph has many peaks that is why I was unsuccefull in finding the number of peaks using functions such as findpeaks for the graph below it returns a number of peaks around 3000 whereas I want to have the number 7.
My idea was to do a for or while loop that counts the number of instances where the average is higher than 0.5. So ultimately I want a function that iterates in segments over the graph returns the number of peaks and the range of y index values for which this peak occurs (I think the best way to do this would to save them to a zeros matrix).
link of file data: https://www.dropbox.com/s/vv8vqv28mqzfr9l/Example_data.mat?dl=0
Do you mean you are trying to count the 'on' parts of your data?
You're on the right track using findpeaks. If you scroll to the bottom of the documentation you'll see that you can actually tweak the routine in various ways, for example specifying the minimum distance between peaks, or the minimum difference between a point and its neighbour before it is considered a peak.
By defining the minimum distance between peaks, I detected the following 7 peaks. Code is included below. Alternatively you can play around with the other parameters you can pass into findpeaks.
The only other thing to note is that I took the absolute value of your data.
load('Example_data.mat')
indx = 1:numel(number11);
[pks, locs] = findpeaks(abs(number11), indx, 'MinPeakDistance', 0.25e4);
hold on
plot(number11)
plot(locs,pks, 'rx')
disp(numel(pks))
Related
I'm trying to find the peaks of four magnitude spectrums:
The amplitudes are stored in variable A (one for each plot). When trying to find the peaks and locations using
[peak loc] = findpeaks(A)
I get a matrix with size around 1000 with most of those values being 0!
In the documdntation you will find a parameter 'NPeaks' forcing a maximum number of peaks returned by the function. As an example findpeaks(x,'Npeaks',1) always returns 0 or 1 peak(s)
I have used the (findpeaks) function in Matlab, in order to find the locations and the value of the peaks in the signal.
findpeaks(X_Segments{1});
X_Segments contains the data, here is sample of the figure that I got
As shown in the figure, some of the peaks are very close to each other, therefore, I'd to filter out these peaks (remove them) in order to have Peaks in the signal at regular intervals.
If you pass the parameter MinPeakDistance into the findpeaks function you can set the minimum distance between peaks. In your case:
findpeaks(X_Segments{1}, 'MinPeakDistance', 10);
Alternatively, you may find the MinPeakProminence or threshold parameters useful. See the examples here.
I have about 10000 floating point data, and have read them into a single row matrix.
Now I would like to plot them and show their distribution, would there be some simple functions to do that?
plot() actually plots value with respect to data number...which is not what I want
bar() is similar to what I want, but actually I would like to lower the sample rate and merge neighbor bars which are close enough (e.g. one bar for 0.50-0.55, and one bar for 0.55-0.60, etc) instead of having one single bar for every single data sample.
would there be a function to calculate this distribution by dividing the range into small steps, and outputting the prob density in each step?
Thank you!
hist() would be best. It plots a histogram, with a lot of options which you can see by doc hist, or by checking the Matlab website. Options include a specified number of bins, or a range of bins. This will plot a histogram of 1000 normally random points, with 50 bins.
hist(randn(1000,1),50)
I have a graph with five major peaks. I'd like to find the position and value of the first peak (the one furthest to the right). I have more than 100 different plots of this and the peak grows and shrinks in size in the various plots, and will need to use a for loop. I'm just stuck on determining the x and y values to a large number of significant figures using Matlab code.
Here's one of the many plots:
If you know for sure you're always gonna have 5 peaks I think the FileExchange function extrema will be very helpful, see here.
This will return you the maxima (and minima if needed) in descending order, so the first elements of output zmax and imax are respectively the maximal value and its index, their second elements are the second maximum value and its index and so on.
In the case if the peak you need is always the smallest of the five you'll just need zmax(5) and imax(5) to determine the 5th biggest maximum.
If you have access to Signal Processing Toolbox, findpeaks is the function you are looking for. It can be invoked using different options including number of peaks, which can be helpful when that information is available.
I have a vector that I want to print a histogram of of data for. This data ranges from -100 to +100. The amount of data around the outer edges is insignificant and therefore I don't want to see it. I am most interested in showing data from -20 to +20.
1.) How can I limit that window to print on my histogram?
The amount of data I have at 0 outnumbers of the amount of data I have anywhere in the dataset by a minimum of 10:1. When I print the histogram, the layout of element frequency is lost because it is outnumbered by 0.
2.) Is there a way that I can scale the number of 0 values to be three times the number of -1 entries?
I am expecting an exponential drop of this dataset (in general) and therefore three times the frequency of -1 would easily allow me to see the frequency of the other data.
You can use something like
binCenters = -20:5:20;
[N,X] = hist(V,binCenters);
N = N./scalingVector;
bar(X(2:end-1),N(2:end-1));
Note that the code excludes the extremes of N and X from the bar plot, since they contain the number of values smaller than -20 and larger than 20. Also, by building scalingVector appropriately, you can scale N as you please.
You could also just toss out any values outside the [-20,20] range by using
subsetData=data(abs(data)<=20)
1) You can limit the histogram range you see on the plot by just setting the X axes limits:
xlim([-20 20])
Setting bins in hist command is good, but remember thatall the values outside the bins will fall into the most left and right bin. So you will need to set the axes limits anyway.
2) If there is a big difference between values in different bins, one way is to transform values on Y axes to log scale. Unfortunately just setting Y axes to log (set(gca,'YScale','log')) does not work for bar plot. Calculate the histogram with hist or histc (depending on whether you want to specify bins centers or edges) and log2 the values:
[y, xbin] = hist(data);
bar(xbin, log2(y) ,'hist')
Histogram has a few different methods of calling it. I strongly recommend you read the documentation on the function (doc hist)
What you are looking for is to put in a custom range in the histogram bin. It depends a bit on how many bins you want, but something like this will work.
Data=randn(1000,1)*20;
hist(Data,-20:20);
You could, if you want to, change the frequency of the binning as well. You could also change the axis so that you only focus on the range from -20 to 20, using a xaxis([-20 20]) command. You could also ignore the bin at 0, by using an yaxis and limiting the values to exclude the 0 bin. Without knowing what you want exactly, I can only give you suggestions.