need a for loop that displays value at each point of x.
조회 수: 2 (최근 30일)
이전 댓글 표시
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1142480/image.png)
I need to write a for loop that performs the same calculation as cumtrapz. I have written this code to solve for the total trapezoid value but I am stuck on how to get it to work for for all the points of x.
댓글 수: 0
채택된 답변
Torsten
2022년 10월 2일
편집: Torsten
2022년 10월 2일
But I already gave you the formulae how to code "cumtrapz":
0 = ctrapz(1)
[f(x0)+f(x1)]/2 * (x1-x0) = ctrapz(2)
[f(x0)+f(x1)] / 2 *(x1-x0) + [f(x1)+f(x2)]/2 * (x2-x1) = ctrapz(3),
[f(x0)+f(x1)] / 2 *(x1-x0) + [f(x1)+f(x2)]/2 * (x2-x1) + [f(x2)+f(x3)]/2 * (x3-x2) = ctrapz(4)
...
[f(x0)+f(x1)] / 2 *(x1-x0) + [f(x1)+f(x2)]/2 * (x2-x1) + [f(x2)+f(x3)]/2 * (x3-x2) + ... + [f(x19) + f(x20)]/2 * (x20-x19) = ctrapz(21)
Here they are again with the integration of exp(x) in [0 1] as example:
x = 0:0.1:1;
y = exp(x);
ctrapz = zeros(1,numel(x));
for i = 1:numel(x)-1
ctrapz(i+1) = ctrapz(i) + (y(i)+y(i+1))/2 * (x(i+1)-x(i));
end
hold on
plot(x,y-1)
plot(x,ctrapz)
hold off
댓글 수: 2
추가 답변 (1개)
Walter Roberson
2022년 10월 2일
You are calculating with floating point coefficients in two different ways. You are using == to test equality, which tests for bit-for-bit them being the same value (with the exception that -0 and 0 are treated as equal). Because they are calculated different ways, it is to be expected that they might not give exactly the same answer, that the last couple of bits might be different.
By the way, you can make the logic more compact:
if m == 1 || m == length(Q2y)
TotalTrapVal(m,1) = Q2y(m);
else
stuff
end
댓글 수: 0
참고 항목
카테고리
Help Center 및 File Exchange에서 Loops and Conditional Statements에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!