I need to create a vector from a symbolic polynomial function,but when i use sym2poly command, matlab tells me it is not a polynomial, how should i do?

Question

sebastiano della gatta 2021-12-16

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1612445-i-need-to-create-a-vector-from-a-symbolic-polynomial-function-but-when-i-use-sym2poly-command-matla

评论： Star Strider 2021-12-17

f1=(497*c1^2 + 497*c2^2 + 497*c3^2 + 11*(c3 + c1*c2)*(c2 - c1*c3)*(c1^2 + c2^2 + c3^2 + 1) + 497)^2/(103684*(c1^2 + c2^2 + c3^2 + 1)^2) + (136*c1^2 + 136*c2^2 + 136*c3^2 + (11*(c2 - c1*c3)*(c1^2 - c2^2 - c3^2 + 1)*(c1^2 + c2^2 + c3^2 + 1))/2 + 136)^2/(103684*(c1^2 + c2^2 + c3^2 + 1)^2) - 1;

sym2poly(f1)

Error using sym/sym2poly (line 30)

Not a polynomial

why matlab tells me this?

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

Star Strider 2021-12-16

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1612445-i-need-to-create-a-vector-from-a-symbolic-polynomial-function-but-when-i-use-sym2poly-command-matla#answer_856605

在 MATLAB Online 中打开

One option is to use the coeffs function —

syms c1 c2 c3

sympref('AbbreviateOutput',false);

f1=(497*c1^2 + 497*c2^2 + 497*c3^2 + 11*(c3 + c1*c2)*(c2 - c1*c3)*(c1^2 + c2^2 + c3^2 + 1) + 497)^2/(103684*(c1^2 + c2^2 + c3^2 + 1)^2) + (136*c1^2 + 136*c2^2 + 136*c3^2 + (11*(c2 - c1*c3)*(c1^2 - c2^2 - c3^2 + 1)*(c1^2 + c2^2 + c3^2 + 1))/2 + 136)^2/(103684*(c1^2 + c2^2 + c3^2 + 1)^2) - 1

f1 =

f1 = simplify(f1, 500)

f1 =

[f1n, f1d] = numden(f1)

f1n =

f1d =

414736

[f1n_cfs, f1n_trms] = coeffs(f1n) % Numerator Coefficients & Terms

f1n_cfs =

f1n_trms =

[f1n_cfs_all, trms_all] = coeffs(f1, 'All')

f1n_cfs_all(:,:,1) =

f1n_cfs_all(:,:,2) =

f1n_cfs_all(:,:,3) =

f1n_cfs_all(:,:,4) =

f1n_cfs_all(:,:,5) =

f1n_cfs_all(:,:,6) =

f1n_cfs_all(:,:,7) =

trms_all(:,:,1) =

trms_all(:,:,2) =

trms_all(:,:,3) =

trms_all(:,:,4) =

trms_all(:,:,5) =

trms_all(:,:,6) =

trms_all(:,:,7) =

That is as completely and thoroughly as it is possible to decompose this polynomial expression.

.

2 个评论
显示无隐藏无

sebastiano della gatta 2021-12-17

thank you for the answer but I don't want to completely decompose the polynomial, I just need the vector of this function because then I have to apply the grobner bases to arrive at my solution.

Star Strider 2021-12-17

As always, my pleasure!

The first coeffs call then:

[f1n_cfs, f1n_trms] = coeffs(f1n)

is likely as close as it is possible to get. MATLAB inteprets ‘polynomial’ as a univariate polynomial, the reason the sym2poly call fails.

.

请先登录，再进行评论。

Answer 2

sebastiano della gatta 2021-12-17

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1612445-i-need-to-create-a-vector-from-a-symbolic-polynomial-function-but-when-i-use-sym2poly-command-matla#answer_857330

thank you. I have the last question. Can i compute groebner basis from f1? (The first function that I put in the first question).

3 个评论
显示 1更早的评论隐藏 1更早的评论

sebastiano della gatta 2021-12-17

thanks for all.

Star Strider 2021-12-17

As always, my pleasure!

.

请先登录，再进行评论。

I need to create a vector from a symbolic polynomial function,but when i use sym2poly command, matlab tells me it is not a polynomial, how should i do?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

2 个评论
显示无隐藏无

更多回答（1 个）

3 个评论
显示 1更早的评论隐藏 1更早的评论

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

I need to create a vector from a symbolic polynomial function,but when i use sym2poly command, matlab tells me it is not a polynomial, how should i do?

0 个评论 显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

2 个评论 显示 无隐藏 无

更多回答（1 个）

3 个评论 显示 1更早的评论隐藏 1更早的评论

另请参阅

类别

标签

产品

版本

Community Treasure Hunt

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

2 个评论
显示无隐藏无

3 个评论
显示 1更早的评论隐藏 1更早的评论