Normalize and integrate a curve

Hello!

If I want to normalize and integrate this curve, how should I do it?

clc
clear all
Data1=importdata('J30.txt');
x=Data1(:,1);
y=Data1(:,2);
plot(x,y)

[John D'Errico]

trapz won't integrate it? Gosh, I thought it was supposed to do that.

What does normalize mean to you? Divide by the integral perhaps?

[Pouyan Msgn]

yes, If I want to devide by the integral how should I do?

Answer 1

[Image Analyst]

Try this:

% Initialization steps.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

Data1=importdata('J30.txt');
x=Data1(:,1);
y=Data1(:,2);

% Plot original data.
subplot(3, 1, 1);
plot(x, y, 'LineWidth', 2);
grid on
title('Original data', 'FontSize', fontSize);

% Normalize by dividing by y Max
y2 = y / max(y);
% Plot normalized data.
subplot(3, 1, 2);
plot(x, y2, 'LineWidth', 2);
grid on
title('Normalized by Max Y signal', 'FontSize', fontSize);

% Find the area under the original y curve
area = trapz(y)
% Normalize by dividing by y Max
y3 = y / area;
area3 = trapz(y3)
% Plot normalized data.
subplot(3, 1, 3);
plot(x, y3, 'LineWidth', 2);
grid on
title('Normalized by Area under the curve', 'FontSize', fontSize);

[Pouyan Msgn]

Thank you for the help! but one question why do you integrate by y and not both vectors?

I tried first with

clc

clear all

Data1=importdata('J30.txt');

x=Data1(:,1);

y=Data1(:,2);

X=x/norm(x);

Y=y/norm(y);

I=trapz(X,Y);

But why it is not correct ?

[Image Analyst]

Because when I used trapz(x, y) it mysteriously gave me a negative area!

[Star Strider]

The negative area is due to the independent variable decending (essentially going right-to-left rather than left-to-right).

Data1 = flipud(Data1);

will likely result in a positive area.

[Image Analyst]

Thanks Star. I didn't notice that x was going in the opposite direction.

[Star Strider]

My pleasure. That’s always the first thing I check if the result looks strange!

[Pouyan Msgn]

but how should the answer be right now? Must I normalize the x axis?

[Image Analyst]

We don't know exactly what you want. Only you know that. I made two guesses as to what you possibly might want. Does any of them look like what you might want?