Integrating above and below x axis separately

I have 90 trials of walking data that vary in duration, but the longest lasting 93 timestamps (so, I have a 93X90 matrix named Powers). Below is a plot of one trial, where the x axis is time and the y axis is Joint Power:

I am wanting to integrate the curve below and above the x axis separately so that I have the total positive and negative work. I have tried using if end statements and the trapz function but that didnt seem to work and I'm not sure why.

if Powers > 0 
    PosWork = trapz(Powers,1)
end

if Powers < 0
    NegWork = trapz(Powers, 1)
end

How would I integrate a curve below and above the x axis separately for every column of my matrix? Any help is appreciated. Thank you in advance.

Answer 1

[Star Strider]

With no if blocks:

t = linspace(0, 10);                                        % Independent Variable
Powers = sin(2*pi*t) + randn(size(t))*0.1;                  % Signal (With Some Noise)


Poswork = trapz(t, Powers .* (Powers > 0));                 % With Independent Variable (More Accurate)
Negwork = trapz(t, Powers .* (Powers < 0));                 % With Independent Variable (More Accurate)

Poswork = trapz(Powers(:) .* (Powers(:) > 0), 1);           % With Point Spacing, Forcing Column Vector
Negwork = trapz(Powers(:) .* (Powers(:) < 0), 1);           % With Point Spacing, Forcing Column Vector

.

[LRW]

This worked. Thank you!

[Star Strider]

As always, my pleasure!

Answer 2

[Image Analyst]

Try

if Powers > 0 
    p2 = Powers
    p2(p2 <= 0) = 0; % Zero out negative going values.
    PosWork = trapz(p2, 1)
end

if Powers < 0
    p2 = Powers
    p2(p2 >= 0) = 0; % Zero out positive going values.
    NegWork = trapz(p2, 1)
end

[LRW]

Thank you for your reply! I tried this. But, it doesn't seem to be storing the values. After running the script, I don't get any variables in my workspace named PosWork or NegWork.

I am trying to do this same process for every column of my data. Do I need to include a for loop?

[Image Analyst]

What columns? You show a single line plot. If it's not storing any values, then it's not getting into the if block. Not sure why those are there anyway. Get rid of them

p2 = Powers
p2(p2 <= 0) = 0; % Zero out negative going values.
PosWork = trapz(p2, 1)
p2 = Powers
p2(p2 >= 0) = 0; % Zero out positive going values.
NegWork = trapz(p2, 1)

You forgot to attach any data so how can I help?

TUTORIAL: How to ask a question (on Answers) and get a fast answer

[LRW]

My apologies for not attaching any data. I thought if I adequately explained my data that would be sufficient.

Attached is a .csv file containing my data. The first column is time or the independent variable. Then columns 2 - 81 are each a separate trial of walking data. I am wanting to calculate the total positive and negative work for each trial.

If you are still willing to help me, I would greatly appreciate it. I tried getting rid of the if block and that didn't appear to work.

[Image Analyst]

Looks like you no longer need help since you accepted Star's answer.

[Image Analyst]

OK, I did it because it doesn't look like Star's solution reads in your data and does it over all your columns like you wanted. Try this:

clc;    % Clear the command window.
clear all;
close all;
workspace;  % Make sure the workspace panel is showing.
format short g;
format compact;
fontSize = 15;
fprintf('Beginning to run %s.m ...\n', mfilename);

Powers = csvread('Powers.csv')
x = Powers(:, 1);
subplot(1, 2, 1);
[rows, columns] = size(Powers);
for col = 2 : columns
	thisY = Powers(:, col);
	thisX = x;
	% Remove any nans
	nanInidexes = isnan(thisY);
	thisY(nanInidexes) = [];
	thisX(nanInidexes) = [];
	
	p2 = thisY; % Initialize
	% Plot it.
	plot(thisX, thisY, '-');
	grid on;
	hold on;
	
	p2(thisY <= 0) = 0; % Zero out negative going values.
	PosWork(col-1) = trapz(p2, 1)
	p2 = thisY; % Re-initialize.
	p2(thisY >= 0) = 0; % Zero out positive going values.
	NegWork(col-1) = trapz(p2, 1)
end
title('Individual Data', 'fontSize', fontSize);
subplot(1, 2, 2);
plot(PosWork, 'b-', 'LineWidth', 2);
hold on;
plot(NegWork, 'b-', 'LineWidth', 2);
grid on;
xlabel('x', 'fontSize', fontSize);
ylabel('Work', 'fontSize', fontSize);
legend('Positive Work', 'Negative Work');
title('Work', 'fontSize', fontSize);
g = gcf;
g.WindowState = 'maximized';
fprintf('Done running %s.m ...\n', mfilename);