Why does symbolic integration return the wrong answer for this integral?

13 次查看（过去 30 天）
Gareth Fuller
Gareth Fuller 2021-2-23
评论： Walter Roberson 2021-2-23
Hello! I'm trying to integrate 1/(1-x)^2 with the bounds 0 to x.
Now, other sources (Like WolframAlpha) return the result as -x/(x-1). However, MATLAB returns inf.
Can anyone explain why this would be?
syms x
expr = 1/(1-x)^2
int(expr, 0, x)
ans =
Inf

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2021-2-23
Ran in:
syms x a
expr = 1/(1-x)^2
expr = 
F = int(expr, x, 0, a)
F = 
subs(F,a,x)
ans = 
  2 个评论
Gareth Fuller
Gareth Fuller 2021-2-23
That works- All I've got to do to get the desired result is some shuffling around of terms.
I'm curious as to why the Subs step is needed, and why it can't get the piecewise function with int(expr,0,x).
Thanks for providing a solution- that certainly helped me out.
Have a wonderful day!
Walter Roberson
Walter Roberson 2021-2-23
I am not sure. My expectation was that I would be able to control the output by adding in an assume() or tossing in an 'IgnoreAnalyticConstraints' option, but those did not work.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Numerical Integration and Differentiation 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by