MATLAB: Plot extreme values on a time series

maximumsplotsubplot

Hi, I have the attached plots. I would like to mark the maximum and minimum value with a marker and show the values on a legend.

Thanks

Best Answer

Use the max and min functions with two outputs to get the first instance of the maximum and minimum. Then use the second (index) output to find the value of time where it occurred:

[ymax,maxidx] = max(y);
[ymin,minidx] = min(y);
figure(1)
plot(time, y)
hold on
plot(time(maxidx), ymax, '^r')
plot(time(minidx), ymin, 'vr')
hold off
grid

If you have more than one values for the maximum or minimum, use the find function:

maxidx = find(y == max(y));

and the plot calls then change to:

plot(time(maxidx), y(maxidx), '^r')

and the same for the minima.

NOTE — This is UNTESTED CODE but should work.

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MATLAB: Finding the maximum y value for one graph

I cannot run your code because I do not have your ODE function. However when I create an ODE function to work with it, you code appears to work.

If you want the index of the first maximum for each, ask max to return both outputs:

[ymax2,imax2] = max(y(:,1));
[ymax1,imax1] = max(y(:,2));

The second one is the index where the first maximum occurs. You can correctly reference the corresponding time that way:

ymax2=max(y(imax1,1));

MATLAB: Multiple variable analysis representation

[A, B, C, D] = ndgrid(1:10, 5:5:50, 0.1:0.1:1, 3:3:30);
y = A .* x.^3 + B .* x.^2 + C .* x + D;
[miny, minidx] = min(y(:));
[maxy, maxidx] = max(y(:));
parms_at_min = [A(minidx); B(minidx); C(minidx); D(minidx)];
parms_at_max = [A(maxidx); B(maxidx); C(maxidx); D(maxidx)];

If you have multiple X values then

numx = length(x);
[A, B, C, D, X] = ndgrid(1:10, 5:5:50, 0.1:0.1:1, 3:3:30, x);
y = A .* X.^3 + B .* X.^2 + C .* X + D;
rsy = reshape(y,[], numx);
[miny, minidx] = min(rsy);  %first dimension

[maxy, maxidx] = max(rsy);  %first dimension
parms_at_min = [A(minidx); B(minidx); C(minidx); D(minidx)];
parms_at_max = [A(maxidx), B(maxidx), C(maxidx), D(maxidx)];

I make no claims that this is the most efficient way.

Best Answer

Related Solutions

MATLAB: Finding the maximum y value for one graph

MATLAB: Multiple variable analysis representation

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