finding maximum value of a plot

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.

Answer 1

[Eli Cuellar]

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!

[Danish Sarfaraz]

very helpful thanks

[Aero32]

is there a way to find a certain percentage of the max and the time that it occurs by using this?

[William Eriksson Selin]

Yes

[Daniel Murphy]

Thanks man

[Michael Goshen]

What if you wanted a dotted line to go up to your 'o' marker?

[Voss]

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')

Answer 2

[madhan ravi]

[max_value,index]=max(b1)