I'm trying to find the local maxima of a data set using the findpeaks() function and so far I have this code:
[pks, locs] = findpeaks(signal);
max_times = zeros(size(locs));
if n = 1:size(locs);
max_times(n) = (times(locs(n)));
end
What am I trying to do? Well I have a set of signal data and the corresponding times. I want to get the local maxima values and output two vectors; the maxima signal values and the times that they occured.
How am I doing it? I'm using the findpeaks function to find the peaks (pks) and location (locs) of the maxima. I'm then setting up a blank array the same length as the locs vector and then using an if loop to fill up the empty max_times(n) vector with the times that the maxima occur
The problem? I keep getting this errorExpression or statement is incomplete or incorrect. about my if loop. I don't understand what this means/ how do I solve this problem/ edit my code to get it to do what I want?
Thanks for any help!
What you are thinking is totally wrong.
If is not a loop its a conditional statement
what you want here is a for loop
for n = 1:size(locs)
% your code
end
also times take two parameter and you should figure it out yourself what it should be
Related
I'm using the findpeaks method in Matlab to find peaks. I have a matrix(Peak) of 260x601 where its 260 different trials over 601 time points. I have a separate vector for the actual time (called TimeVec).
I'm using a for loop to loop over the trials.
for i = 1:size(Peak,1)
[pks(i),locs(i)]=findpeaks(Peak(i,:),timeVec,'MinPeakHeight',1);
end
The problem is that each trial could have a different number of peaks therefore it's trying to combine a different number of columns to each iteration. How can I get around this?
This is a short and not fully efficient method:
fp = #(k) findpeaks(Peak(k,:),timeVec,'MinPeakHeight',1);
[pks,locs] = arrayfun(fp,1:size(Peak,1),'UniformOutput',false);
it will be a bit faster with a for loop, but it worth changing this only if you have more data:
[pks,locs] = deal(cell(size(Peak,1),1));
for k = 1:size(Peak,1)
[pks{k},locs{k}] = findpeaks(Peak(k,:),timeVec,'MinPeakHeight',1);
end
for further manipulations on that, use #excaza advice and read the cell array docs.
I'm trying the following and is not working. Could someone help me on this?
A=rand(1,4,5);
peak_num=zeros(5,4);
for w=1:5
peak_num(w,:)=peakfinder(A(1,1:4,w))
end
peak_num;
in this case the vector of peaks found for each w has a different size.
Thanks
I haven't really taken a look at the internals of the peakfinder function but if you make sure that it does not output a vector with more than 4 elements this is a workaround:
A=rand(1,4,5);
peak_num=zeros(5,4);
for w=1:5
temp = peakfinder(A(1,1:4,w));
peak_num(w, 1:length(temp) ) = temp
end
peak_num;
It sets the first elements to the return values and keeps the others being zero.
I have a problem with the following code. I want to store all the values I am creating in the for loop below so that I can make a plot of it. I have tried several things, but nothing works. Does anyone know a simple method to create a vector of the results and then plot them?
dx=0.1;
t=1;
e=1;
for x=-1:dx:1
lower_bound=-100;
upper_bound=x/(sqrt(4*t*e));
e=1;
u=(1/sqrt(pi))*quad(#integ,lower_bound,upper_bound);
plot(x,u)
hold on
end
hold off
I would like to use as much of this matlab code as possible.
dx=0.1;
t=1;
e=1;
xval=[-1:dx:1].';
upper_bound = zeros(numel(xval),1);
u = zeros(numel(xval),1);
for ii=1:numel(xval)
x = xval(ii)
lower_bound=-100;
upper_bound(ii,1)=x/(sqrt(4*t*e));
u(ii,1)=(1/sqrt(pi))*quad(#integ,lower_bound,upper_bound(ii));
end
figure;
plot(xval,u)
by adding the (ii) behind your statements it saves your variables in an array. I did not use that on your lower_bound since it is a constant.
Note that I first created an array xval and called that with integers in ii, since subscriptindices must be positive integers in MATLAB. I also initialised both upper_bound and u by creating a zero matrix before the loop executes. This is handy since extending an existing vector is very memory and time consuming in MATLAB and since you know how big they will get (same number of elements as xval) you might as well use that.
I also got the plot call outside the loop, to prevent you from plotting 21 blue lines in 1 plot.
I'm trying to split an audio file into 30 millisecond disjoint intervals using Matlab. I have the following code at the moment:
clear all
close all
% load the audio file and get its sampling rate
[y, fs] = audioread('JFK_ES156.wav');
for m = 1 : 6000
[t(m), fs] = audioread('JFK_ES156.wav', [(m*(0.03)*fs) ((m+1)*(0.03)*fs)]);
end
But the problem is that I get the following error:
In an assignment A(I) = B, the number of elements in B and I
must be the same.
Error in splitting (line 12)
[t(m), fs] = audioread('JFK_ES156.wav', [(m*(0.03)*fs)
((m+1)*(0.03)*fs)]);
I don't see why there's a mismatch in the number of elements in B and I and how to solve this. How can I get past this error? Or is there just an easier way to split the audio file (maybe another function I don't know about or something)?
I think the easiest way to split audio is to just load it and use the vec2mat function. so you would have something like this;
[X,Fs] = audioread('JFK_ES156.wav');
%Calculate how many samples you need to capture 30ms of audio
matSize = Fs*0.3;
%Pay attention to that apostrophe. Makes sure samples are stored in columns
%rather than rows.
output = vec2mat(x,matSize)';
%You can now have your audio split up into the different columns of your matrix.
%You can call them by using the column calling command for matrices.
%Plot first 30ms of audio
plot(output(:,1));
%You can join the audio back together using this command.
output = output(:);
Hope that helps. Another good thing about this method is that it keeps all your data in one place!
Edit : One thing I thought of, you may get a problem with this depending on your vector size. But I think vec2mat actually zeroPads your vector. Not a big thing, but if you're moving back and forth between the two, then it might be a good idea to have another variable that stores the original length of your signal.
You should just use the variable y and reshape it to form your split audio. For example,
chunk_size = fs*0.03;
y_chunks = reshape(y, chunk_size, 6000);
That will give you a matrix with each column a 30 ms chunk. This code will also be faster than reading small segments from file in a loop.
As hiandbaii suggested you could also use cell array. Make sure you clear your existing variables before that. Not clearing the array t is probably the reason you got the error "Cell contents assignment to a non-cell array object."
Your original error is because you cannot assign a vector with scalar indexing. That is, 'm' is a scalar, but your audioread call is returning a vector. This is what the error says about mismatch in size of I and B. You could also fix that by making t a 2-D array and use an assignment like
[t(m,:), fs] =
It appears that each 30 ms segment is not equal to one sample. That would be the only case where your code works. i.e. 0.03*fs != 1.
You could try using cells instead.. i.e. replace t(m) with t{m}
I've looked around on the internet a bit and cannot seem to find the answer to this question. I want to declare a vector in matlab and then have a for loop that will add an element to the vector each time I go through the for loop.
This is what I've tried and it doesn't seem to be working
vector[];
for k = 1 ; 10
%calculate some value
%calculated value stored in temp variable
vector(k) = temp;
end
This does not work. Does anybody know how to solve this issue?
As ypnos said, you don't need to declare the vector variable upfront. For example if you did:
vector(50) = 1;
MATLAB would make a vector of length 50 with the 50th value being 1. If you want to improve performance and want to create a vector of the proper size beforehand then do the following:
vector = zeros(10, 1);
The code as you have it (as long as you fix the loop as ypnos said) will work, except for how you declare vector, which is not correct. I bet you are getting the error message: "Error: Unbalanced or unexpected parenthesis or bracket." You do not specify whether a variable is a matrix/vector in MATLAB.
vector = [vector; temp];
or
vector(end+1) = temp;