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?

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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?

採用された回答

Star Strider
Star Strider 2021 年 12 月 16 日
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.
.
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Star Strider
Star Strider 2021 年 12 月 17 日
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.
.

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sebastiano della gatta
sebastiano della gatta 2021 年 12 月 17 日
thank you. I have the last question. Can i compute groebner basis from f1? (The first function that I put in the first question).
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