Finite Integral with periodic values of x

Question

Manish Kumar 2019-3-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/449598-finite-integral-with-periodic-values-of-x

评论： Torsten 2019-3-12

Book1.xlsx

Dear All,

Range of my x axis is 0.3 to 4.5. I want to integrate my x and y data with x range from 0.3 to 4.5 with the interval of 0.01. First column of the excel sheet is x and 2nd column is y. I write a code as below:

for i = 0.3:4.5:0.01

idx = (x>=i & x<=4.5);

xp = x(idx);

yp = y(idx);

f(i,:)=trapz(xp,yp)

end

I need improvement on this script. Please help.

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Answer 1

Torsten 2019-3-12

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/449598-finite-integral-with-periodic-values-of-x#answer_364979

编辑：Torsten 2019-3-12

idx = (x>=0.3 & x<=4.5);
xp = x(idx);
yp = y(idx);
F = cumtrapz(xp,yp);
F = F(end) - F;
plot(xp,F)

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Manish Kumar 2019-3-12

编辑：Manish Kumar 2019-3-12

i want to calculate the integral by varying the limit. Lower limit is 0.3, 0.31,0.32,0.33....4.5 and upper limit is 4.5

Torsten 2019-3-12

If you insist varying the lower limit by a fixed amount, you can use

index = 0;
for iter = 0.3:0.01:4.5
  index = index + 1;
  idx = (x>=iter & x<=4.5);
  xp = x(idx);
  yp = y(idx);
  xiter(index) = iter;
  Fiter(index) = trapz(xp,yp);
end
plot(xiter,Fiter)