using find-command to find max or min value

Question

Moustafa Abedel Fattah 2022-6-26

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评论： Moustafa Abedel Fattah 2022-6-28

Delson Max_gBt_gradient.jpg

Please I need your help to estimate the value of min or max of abs(Y) and its corresponding (X) for attached curve (X versus X ) using (find)-command. In addition want plot a line of corresponding (X) and (Y).

Thanks in advance for all.

Best Regards;

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Moustafa Abedel Fattah 2022-6-26

Thanks a lot for your quick response as usual. It is works very good and I will more appreciate if you solve it also with (find) command.

Thanks in advance

Best Regards;

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Answer 1

Star Strider 2022-6-26

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This is relatively straightforward. Use max with two outputs:

x = 0:13;

y = randi(25,1,14)/100;

[ymax,idx] = max(y)

ymax = 0.2400

idx = 13

figure

plot(x, y)

hold on

plot([1 1]*x(idx), [min(ylim) ymax], '-r')

plot([0 x(idx)], [1 1]*ymax, '-r')

hold off

grid

Experiment with your data.

.

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Star Strider 2022-6-27

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As always, my pleasure!

Using find is straghtforward —

x = 0:13;

y = randi(25,1,14)/100;

idx = find(y == max(y))

idx = 10

figure

plot(x, y)

hold on

plot([1 1]*x(idx), [min(ylim) y(idx)], '-r')

plot([0 x(idx)], [1 1]*y(idx), '-r')

hold off

grid

That requires essentially the same code.

.

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Answer 2

Image Analyst 2022-6-26

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I prefer using the find function in combination to find max and min locations. The reason being if the max occurs at more than one location, max only gives you the location of the first one. I've asked them for many, many years to return the index(es) of all max in the vactor.

y = [1 3 2 3 0] % Max at index 2 and 4
y = 1×5
     1     3     2     3     0
[maxValue, indexes] = max(y) % Only gives you the one at index 2 not at 4.
maxValue = 3
indexes = 2