How do you remove a trend from data without using the 'detrend' function?

%I have imported data into matlab and plotted the data onto a graph. I am having difficulty removing the trend without using the 'detrend' function. Any ideas on how to start this process?

A = dlmread('signal_1.txt');

x= A(:,1);

y= A(:,2);

plot(x,y);

xlabel('Time(s)');

ylabel('Amplitude');

How would i achieve this goal?

Answer 1

[the cyclist]

Usually, when someone "doesn't want" to use a function, it means that it is homework, and they are not allowed to use a function, and are instead trying to learn something.

Here is a hint: In base MATLAB, you could use the polyfit function to find the line of best fit. That's the trend line. Then figure out how to subtract it out of your data.

Answer 2

[Image Analyst]

You could use the findpeaks function to find valleys in the data, then interpolate those everywhere with interp1

Here's an untested start. Adapt as needed.

[valleyValues, indexes] = findpeaks(-y);
yBaseline = interp1(x(indexes), -valueValues, x);
yCorrected = y - yBaseline;