how can i Calculate area of plotted data using trapz in matlab?

have data from csv file. i want to calculate area under plot using trapz but im not sure if trapz is calculating from zero on y-axis as a reference or the starting point of x&y-axes. How can i calculate this area subtracting region below minimum point?

code is below data=csvread('test_1.csv'); new_data=smoothdata(data); x_col1=new_data(:,1); y_col2=new_data(:,2); figure('Name','Smoothed_waveform') plot(x_col1,y_col2,'r')

title('Induced emf') xlabel('Time (s)') ylabel('Amplitude')

grid on grid minor

max_y= max(new_data(:,2))% maximum value of signal min_y= min(new_data(:,2))% minimum value of signal amplitude= (max_y-min_y) %amplitude of signal area_2 = trapz(new_data(:,1),new_data(:,2))

graph

Answer 1

[Dimitris Kalogiros]

Before using trapz, do the following

new_data(:,2)=new_data(:,2)-min(new_data(:,2));

this shifts all of your graph upwards, so minimum value would be on xx' axis.

[jasper kansiime]

yes. this is better. Thanks so much. Results are as expected now.