MATLAB: How to define one cycle from the data by taking the max value?

array

Right now I am taking a .txt file and have defined f as a whole column from the .txt file that was extracted from a DAQ in labview. My code isn't working and the error says:

"Subscript indices must either be real positive integers or logicals."

I read some questions and threads about this already but the fixes didn't work for me.

[Max_Value_Force,maxI] = max(f(:))
Time_Max_Force = t(maxI)
onecycle = f((Time_Max_Force-25):(Time_Max_Force+25))

Thank you so much.

Best Answer

Try this:

onecycle = f((maxI-25):(maxI+25));

Indices in MATLAB must be integers greater than zero. I am assuming her that ‘maxI’ is greater than or equal to 26, and is at least 26 less than the length of your ‘f’ vector.

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MATLAB: How to pull Time values from the found indicies of Force

indBefore10 contains only the index, not the force itself, you have to give then back to the force array to actually get the result, that's why max(indBefore10) will give you unreasonable results. You also have more a couple of errors in your code that are based in a confusion between index/value. A way to do it that works is:

indBefore10 = find(force<10); %Finds all indicies which the force value is <10 .
[maxForce10, maxIndForce10] = max(force(indBefore10)) ; % Get the force values belonging to the indices
[minValForce10, minIndForce10] = min(force(indBefore10)); 
% Correct index (since they are founded based in the indBefore10
maxIndForce10   = indBefore10(maxIndForce10);
maxIndForce10   = indBefore10(minIndForce10);
MinTimeInd = time(minIndForce10) ; % time is most probably not integer, so time==Index will give you wrong results. This way will always work
MaxTimeInd = time(maxIndForce10);
TimeDiff = MaxTimeInd - MinTimeInd

MATLAB: Help creating Z from X and Y for a contour plot

You need the invaluable assistance of the meshgrid function to make your dreams reality:

figure(3)
force_amplitude=1:13;
force_time=0:0.05:0.6;
[F_A, F_T] = meshgrid(force_amplitude, force_time);
energy_consumption = @(force_amplitude, force_time) 20.093*12.5*((1.27./(force_amplitude.*force_time))+force_time);
C = @(force_amplitude, force_time) (1.27./(force_amplitude.*force_time))-force_time;
contour(force_amplitude,force_time,energy_consumption(F_A, F_T))
xlabel('Force Amplitude')
ylabel('Force Time')

I created ‘energy_consumption’ (and ‘C’) as anonymous functions for convenience, then after vectorising them, called them from within your contour call. You can certainly create separate ‘Z’ matrices, for example:

Z = energy_consumption(F_A, F_T);

and then plot it.

If you are not already familiar with them, see the documentation on Anonymous Functions (link) for a full discussion.

In your code, you do not need the square brackets around the vectors, although if they make your code more readable for you, use them.

Best Answer

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MATLAB: How to pull Time values from the found indicies of Force

MATLAB: Help creating Z from X and Y for a contour plot

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