"Subscript indices must either be real positive integers or logicals" error while using trapz function

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ishita agrawal 2018-5-19

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评论： Image Analyst 2018-5-19

Data.csv

Hello, I am using following code to calculate area under the peak.

            D = amplitude(:);
            l = 59;
            chg(1) = 1;
            chg(2) = l;         
            for k1 = 1:numel(chg)-1
                segment_area_1k1(a,j) = trapz(chg(k1:k1+1), D(chg(k1:k1+1)));
            end  
        end

The code upon run shows error "subscript indices must either be real positive integers or logicals". I have attached amplitude data for reference. Can anyone solve this problem?

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Answer 1

Ameer Hamza 2018-5-19

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编辑：Ameer Hamza 2018-5-19

在 MATLAB Online 中打开

What are the values of a and j? They must be a positive integer. Also if you just want to calculate the area under the curve, then pass an entire vector to trapz()

area = trapz(D);

If you want to get segmented area, you can avoid for loop altogether. A better approach is to do it like this

segmentedArea = diff(cumtrapz(D))

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ishita agrawal 2018-5-19

Actually, this code worked perfectly for other datasets. This time, it is working for some values in the dataset and then this error occurred.

There is something I want to ask. When I tried your code (trapz(D)), the value of calculated area was different than what I calculated using my code. I couldn't understand the reason.

Image Analyst 2018-5-19

Give your complete code, including the code where you read in the data file, and your complete error message, including line numbers and ALL the red text.

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