How to obtain an absorption spectrum from a derivative spectrum?

I have a derivative spectrum represented with 128 points and need to integrate the spectrum to get absorption spectrum with 128 points. How to do this?

Answer 1

[Star Strider]

See if the trapz or cumtrapz functions will do what you want.

[dsp]

It doesn't work.

[Star Strider]

Yes it does.

How did you write your code?

What result do you want?

[dsp]

a=[ a1, a2, ...... a128];

b=trapz(a); % gives a single point output

c=cumtrapz(a); %gives 128 point output

Image attached is for representative purpose only.

[Walter Roberson]

cumsum(a)

[dsp]

cumsum also gives almost same plot as cumtrapz.

[Walter Roberson]

When I try with

a = [0 0 8 0 -8 0 7 0 -7 0 9 0 -3 0]

then

plot(cumtrapz(a))

gives me pretty much the shape you are looking for.

The cumtrapz result you are seeing would be consistent with the first negative not being sufficient to balance out the first positive. If you go up but do not come down all the way, you do expect to be left part way up.

[dsp]

@walter, pls add your answer spearatly, so I can accept it.