MATLAB: How to locate the index of the maximum value in a given range

data acquisitionindexindexingMATLABmaximum

Suppose we have two vectors

t= [ 1 2 3 4 5 6 7 8 9 10 11]; % time values

y = [1 2 3 4 5 7 5 4 3 2 1]; % a dependent variable

We can find the max value of y, by max(y), here it is 7. How can we locate the index i of 7 and value the corresponding value of t at idex i? Basically I am trying to locate a peak maximum and its corresponding time.

Thanks

Best Answer

Use the 2nd output of the max function:

[p,i] = max(y);

p is the max value, i is the index of the max value

t(i) is the value of t at the same point as the max of y

Related Solutions

MATLAB: How to extract two equal maximum values at different index

index=find(A==max(A))

This should give you the indexes.

MATLAB: Locating Peaks Naively

In case you don't have the Signal Processing Toolbox, or its findpeaks function is not general enough, you could try the following function - though I don't claim it's the the fastest way possible!

function peaks = peakfind(v, x)
%PEAKFIND finds local peaks
%   PEAKS = PEAKFIND(V, X) returns the indices of elements of vector V such
%   that V(P) is greater than V(P + K) for all integers K such that K >=
%   -X, K <= X and K ~= 0. Only peaks for which P > X and P < length(V)+1-X
%   are returned.
%
%   V must be a row or a column vector. X must be a positive integer. The
%   result is a vector containing the indices P.
% Argument checking omitted for speed.
pks = true;
va = v(x+1 : end);
for k = 1:x
   vb = v(x+1-k : end-k);
   pksa = va > vb;
   pksb = vb > va;
   pks = pks & pksa(1 : end-x) & pksb(1+k : end-x+k);
end
peaks = find(pks) + x;
end

One thing to note: if you define a peak to be an element that is greater than all its neighbours, repeated values in the input vector will never be seen as a peak. So [ 1 100 100 1] (with X=1) has no peaks using your definition. If you want to find such plateaux, you can do it by breaking the symmetry and finding one of the values. In the code above, you could replace "pksb = vb > va" with "pksb = ~pksa" (and amending the description) to achieve this.

Best Answer

Related Solutions

MATLAB: How to extract two equal maximum values at different index

MATLAB: Locating Peaks Naively

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