# finding maximum value of a plot

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Ajay Siddarth on 7 Mar 2019
Edited: Voss on 11 Mar 2022
hi im need to know hoe to find the maximum value of a graph i have plptted in matlab.
the code is something like this:
a1=[1 2 3 4 5 6 7 8 9];
b1=[10 20 5 0 48 46 455 21 32];
plot(a1,b1);
not excatly as above but has many many values of x,y. Now i have got the plot and i need to find the maximum value of the plot i have got.
please help in finding it..maybe a matlab code for the same would be helpfull.

Eli Cuellar on 7 Mar 2019
I will assume you need to find both the maximum value in b1 as well as its corresponding a1 value. All you need to do is use the max() function. The max() function will return both the maximum value, and the index position of the value. You can use the index to extract the corresponding a1.
Example follows:
a1=[1 2 3 4 5 6 7 8 9];
b1=[10 20 5 0 48 46 455 21 32];
[b1_max, index] = max(b1);
a1_max = a1(index);
You can also plot the maximum value as so:
plot(a1, b1, a1_max, b1_max, 'ro')
The 'ro' option tells matlab to plot (a1_max, b1_max) in red, and using an 'o' as marker.
Hope it helps!
Voss on 11 Mar 2022
Edited: Voss on 11 Mar 2022
a1=[1 2 3 4 5 6 7 8 9];
b1=[10 20 5 0 48 46 455 21 32];
[b1_max, index] = max(b1);
a1_max = a1(index);
plot(a1, b1, a1_max, b1_max, 'ro');
hold on
% plot([a1_max a1_max],[0 b1_max],'--m')
% plot([a1_max a1_max],[0 b1_max],'-.m')
plot([a1_max a1_max],[0 b1_max],':m') madhan ravi on 7 Mar 2019
[max_value,index]=max(b1)

R2018b

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