Integrating from polyint(p)
显示 更早的评论
Hi folks!
I have a question regarding univariate integration from the coefficients produced (e.g. 1x8 double) from polynomial integration.
An example code I have is:
[p,S] = polyfit(x,y,N);
q=polyint(p);
At this point, the code produces something like 1x8 double with polynomial coefficients.
But the ultimate integral I would like to compute is an indefinite integral with lower and upper limit being 1 and inf respectively in the form of a fraction:
x/(the polynomial I got for q with x being the variable).
How would I do this?
采纳的回答
John D'Errico
2020-8-4
编辑：John D'Errico
2020-8-4
Sorry, but polyint cannot integrate a rational polynomial, and certainly not over an infinite region. Depending on the roots of the polynomial, it may or may not have an integral.
The simplest way to do your integration is to use the symbolic toolbox.
syms x
P = x^4 + 8*x^3 + 23*x^2 + 28*x + 12;
int(x/P,x,[1,inf])
ans =
log((3*2^(1/2))/8) + 2/3
If you have only the coefficients of the polynomial, you can still do it.
pcoeff = [1 8 23 28 12];
roots(pcoeff)
ans =
-3
-2
-2
-1
So a happy list of roots.
int(x/poly2sym(pcoeff,x),[1,inf])
ans =
log((3*2^(1/2))/8) + 2/3
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Polynomials 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
