How to find the peak value of a graph and how to plot them?

Hi,

I need to find the peak value of each force for the plotted graph and locate it in the graph.

I already use findpeaks but there is no answer and no error informed.

I'm not sure the flow and how to apply the findpeaks command.

Thank you in advance!

X=xlsread('Filtered JCF PHASE 1.xlsx',4,'Z5:AC55');
Y=xlsread('JCF PHASE 1_5UP.xlsx',4,'AN5:AP55');
Z=xlsread('JCF PHASE 1_5DW.xlsx',4,'AN5:AP55');

x1 = X(:,1); %the percentage
y1= X(:,2); %the force value 1
y2= Y(:,1); %the force value 2
y3= Z(:,1); %the force value 3

[pks,locs] = findpeaks (y1,x1);
findpeaks (y1, x1); 

subplot(3,1,1);
plot(x1,y1,'r',x1,y2,'g',x1,y3,'b','Linewidth',3);
title('JCF HIP X');

xlhand = get(gca,'xlabel');
set(xlhand,'string','Percentage of stance phase (%)','fontsize',10)
ylhand = get(gca,'ylabel');
set(ylhand,'string',{'JCF (N)'},'fontsize',10);

Answer 1

[Tommy]

According to the findpeaks() documentation:

"A local peak is a data sample that is either larger than its two neighboring samples or is equal to Inf. Non-Inf signal endpoints are excluded."

and

"If there are no local maxima, then pks is empty."

None of your plots have local maxima. They do each have a maximum value, but these values are all endpoints.

How about just using max()?

[pk_1, loc_1] = max(y1);

[arifahazwani AY]

Thank you for your response.

I want to mark the peak of the curve, and record the value.

The negative and postive sign indicate the position. So, I think I can't use the max as the maximum value is at the end of the curve.

Is there any solution?

Thank you again.

[Tommy]

If you mean you'd like to find local minima in each plot, flip your data upside down while calling findpeaks():

[pk_1,loc_1] = findpeaks(-y1,x1);

[arifahazwani AY]

Thank you.

It's work.! But, how can I plot the value on the graph?

I try with single graph with the code below.

I got the value, but I need to mark on the graph.

Can you please share the script. thank you very much.

X=xlsread('Filtered JCF PHASE 1.xlsx',4,'Z5:AC55');

x1 = X(:,1);
y1= X(:,2);

[pks,locs] = findpeaks(-y1, x1);

figure
plot(x1,y1);
axis tight

hold on
plot(locs, pks, 'r*')
hold off

[Tommy]

Remember that findpeaks() analyzed your data upside-down, so the peak(s) it returns should be flipped.

plot(locs, -pks, 'r*')

[arifahazwani AY]

Noted. thank youu.

[Tommy]

Happy to help!