Symbolic Toolbox: Coefficients and Powers of a polynomial

Question

Christoph 2014-1-23

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/113487-symbolic-toolbox-coefficients-and-powers-of-a-polynomial

回答： Mohamad Hejazi Dinan 2020-7-22

Hey,

suppose I have a (maybe multidimensional) polynomial given in a symbolic way. What I want is all the coefficients of the different terms with knowledge about the power of the variable at this point. So a perfect solution would be something like this

 Input: 3 * x^5 + 2 * x^3 + 23
 Output: Coeffs: [3 2 23], Powers: [5 3 0]
         Or something like the polynomial in matlab, i.e.
         output: [3 0 2 0 0 23]

I actually wrote a small script than can already do what I want:

     syms x
     f = 3 * x^5 + 2 * x^3 + 23 
     [polyCoeffs, mononomials] = coeffs(f)
     % output is 
     % polyCoeffs = [ 3, 2, 23]
     % mononomials = [ x^5, x^3, 1]
     polyPowers = zeros(1, length(mononomials))
     for i=1:length(mononomials)
         polyPowers(i) = length(sym2poly(polyPowers(i))) - 1;
     end

It does the job, but it is very unelegant and - if there are more than one variable in the polynomial - in can get a little bit more complicated. So I'd like to know if anyone has a smarter idea, or if there is something in Matlab I just haven't found yet.

Thanks

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Haroon 2019-1-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/113487-symbolic-toolbox-coefficients-and-powers-of-a-polynomial#answer_357337

在 MATLAB Online 中打开

The above code will not work well. I have modified it and now it is working fine.

syms x
f = 3 * x^5 + 2 * x^3 + 23 
[polyCoeffs, mononomials] = coeffs(f);
poly=sym2poly(f);
polyPowers = zeros(1, length(mononomials));
j=0;
for i=1:length(poly)
    if poly(i)~=0
        j=j+1;
        polyPowers(j)= length(poly)-i;
    end
end
display(polyPowers)