MATLAB Answers


'double' input argument not found using a function

Asked by Joachim
on 22 May 2013
Latest activity Answered by Steven Lord
on 30 Oct 2017


I have got a int16 array (called allAudio) and would like to run the function 'findpeaks' on it. When I write pks = findpeaks(allAudio(1,:)), the error message says: "Error using findpeaks (line 59) Input arguments must be 'double'."

 I don't understand it... Any thoughts? 


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2 Answers

Answer by Iain
on 22 May 2013
 Accepted Answer

findpeaks only operates on numbers that are 64 bit floating point numbers (they're called doubles).

Convert your 16bit integers to double with the function "double".

double_allAudio = double(allAudio);



here's the last bit of the code I wrote to make it work (Had to transpose the matrix)

double_allAudio = double(allAudio);
[pks,locs] = findpeaks(double_allAudio(1,:))

Hello all, But what if we need to specify a certain datatype for the arguments and give the inputs accordingly??

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Answer by Steven Lord
on 30 Oct 2017

In release R2017b we introduced functions islocalmax and islocalmin that support a data input A of double, single, or one of the integer types.

rng default
x = randi(10, 1, 20, 'int8');
ILM = islocalmax(x);
y = [x; ILM]

If you run those four commands, you'll see y is an int8 array and that most of the instances of 10 in x are local maxima, as is one of the instances of 9. To see that graphically:

% NaN values don't get plotted so preallocate then fill the local maxima
z = NaN(size(x));
z(ILM) = x(ILM);
ind = 1:numel(x);
plot(ind, x, '-', ind, z, 'ro');

The red circles correspond to the local maxima. The two plateaus each have one of their two points of equal height marked; see the documentation for islocalmax for more information about how you can customize how that behavior is handled.


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