integral of a piece wise function

Hello

I have just started using matlab and I'm blocked in calculating the integral of a simple piece wise fct , need this integral to calculate the variation of the state of charge of a battery . I tried to use cumsum in a for cycle but it doesn't really work. Can someone please help me or give me some ideas ?

[Walter Roberson]

I recommend that you clean up your code by using elseif

To do an integral use integral() with the waypoints option . But be careful, as that passes vectors of x values and you have to return something the same size. Suggest that you read about "logical indexing"

Answer 1

[Prabhan Purwar]

Hi,

Integral of a function can be calculated either by making use of integral() function or trapz() function, which is more suited for calculating integral of a piecewise function.

Please have a look at the following code:

clc 
close all 
C=10; 
dt=0.1; 
t=0:dt:35; 
for j=1:length(t)    
    if t(j)<=7 
        i(j)=20; 
    else 
        if t(j)<=10 
            i(j)=(t(j)-7)/3*(-35)+20; 
        else 
            if t(j)<=25 
                i(j)=-15; 
            else if t(j)<=35 
                    i(j)=-7.5; 
                end 
            end 
        end 
    end 
end 
  
 for j=1:length(t) 
     I(j)=trapz(t(1:j),i(1:j));   %trapz() function 
     SoC(j)=((C-I(j))./C).*100; 
 end 
 

Please refer to the following links for further information

• https://www.mathworks.com/help/matlab/ref/trapz.html(Trapezoidal numerical integration)
• https://www.mathworks.com/help/matlab/ref/integral.html(Numerical integration)

Hope this helps.

[Giorgio Buoncristiano]

I tried using trapz() but I was not able to correctly use it, thank you! Anyway I did it using cumsum() without a for cycle.