To calculate the area under a series of curves

Hello,

Would you please assist me to calculate the area under different sections of the curves of FR2_.mat? The sections are IC, LR, MS, TS, PS, P50, TOR.

The following lines calculate different sections of the curve like the photo attached to the question.

cycl=13;
for i=1:length(cycl)
    if length(i+5)>length(FR2_)
        break
    end
    LR(i)=find(FR2_(i,:)==max(FR2_(i,1:40)));
   
    for j= LR:70
        if FR2_(i,j+1)> FR2_(i,j)
          MS(i)= find(FR2_(i,:)==( FR2_(i,j)));
        end
        
    end
end 

for i=1:length(cycl)
   
IC(i)=find(FR2_(i,:)==min(FR2_(i,1:3)));
LR(i)=find(FR2_(i,:)==max(FR2_(i,1:40)));
TS(i)=find(FR2_(i,:)==max(FR2_(i,MS(i):85)));
PS(i)=find(FR2_(i,:)==max(FR2_(i,TS(i):99)));
P50(i)=find(FR2_(i,:)==min(FR2_(i,49:51)));
TOR(i)=find(FR2_(i,:)==min(FR2_(i,97:99)));
end

Also, there is a FL2_.mat. I have to find the points of FL2_.mat the correspond to the "IC, LR, MS, TS, PS, P50, TOR" points of FR2_. Then, I have to calculate area under these sections as well.

I appreciate your attention to this question.

Vahid,

Answer 1

[Star Strider]

First, the for loops should both be:

for i = 1:cycl

The areas calculation appears to be straightforward:

for i=1:cycl
AUC = cumtrapz(FR2_(i,:));
IC(i)=find(FR2_(i,:)==min(FR2_(i,1:3)));
LR(i)=find(FR2_(i,:)==max(FR2_(i,1:40)));
TS(i)=find(FR2_(i,:)==max(FR2_(i,MS(i):85)));
PS(i)=find(FR2_(i,:)==max(FR2_(i,TS(i):99)));
P50(i)=find(FR2_(i,:)==min(FR2_(i,49:51)));
TOR(i)=find(FR2_(i,:)==min(FR2_(i,97:99)));
Areas(i,:) = diff(AUC([IC(i) LR(i) TS(i) PS(i) P50(i) TOR(i)]));
end

See if that does what you want.

.

[Vahid Esmaeili]

Dear Star Strider,

Thank you so much for your answer. It worked but I think it was supposed to have a matrix of 13 rows and 6 columns because of [IC(i) LR(i) TS(i) PS(i) P50(i) TOR(i)]. Now I have a matrix of 13 rows and 5 columns with negative values in the 4th column and zero in the 3rd column. Instead, when I type "AUC(MS)" it returns me 13 positive numbers which are acceptable [55.7032 63.3157 73.1998 63.3157 58.7096 60.2274 52.6987 60.2274 61.7615 71.4821 61.7615 57.2032 64.8934] or for "AUC(TS)" it returns [80.2419 78.4683 87.2497 88.9566 85.5214 85.5214 78.4683 88.9566 85.5214 95.5389 83.7743 80.2419 85.5214]. Maybe you can find a solution for it.

Thanks,

[Star Strider]

As always, my pleasure!

The variables:

[IC(i) LR(i) TS(i) PS(i) P50(i) TOR(i)]

appear to be the way you want to partition each of the 13 (1x100) vectors, so I left them that way, and calculated the ‘Areas’ vectors using them, since it was not obvious otherwise how you wanted the curves partitioned. The problem may be the way you calculate those indices.

There are 6 indices spanning almost the entire vector (from 1 to 99), so there would be 5 areas for each vector.

Note that ‘PS’ and ‘TS’ are the same (so a 0 area between them), and the ‘PS’ indices are greater than the ‘P50’ indices, leading to the negative result for that segment.

My code works correctly for the indices you calculated.

.

[Vahid Esmaeili]

I modified the calculation of variables and now everything is OK.

Thanks

[Star Strider]

As always, my pleasure!

I appreciate the follow-up!

Answer 2

[KSSV]

Read about trapz.