How to convert a sym data type to symfun datatype?

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Nagulavancha Sai Preetham 2023-3-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1933820-how-to-convert-a-sym-data-type-to-symfun-datatype

编辑： Manikanta Aditya 2023-3-23

I need to find the value of a function Eq. But the result comes out as an expresssion. The datatype of Eq is sym. How to I change it to symfun to calculate that value?

syms as(q)

A = [1 2 3; 4 5 6; 7 8 9];

B = [2 3 4; 5 6 3; 9 9 10];

P = A - q*B;

Eq = det(P);

C=[3 4 5];

as(q) = 1;

disp(Eq(1));

as = as*poly2sym(C,q)*q;

disp(roots(sym2poly(Eq)));

0.0000 + 0.0000i 0.7949 + 0.2459i 0.7949 - 0.2459i

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Dyuman Joshi 2023-3-23

What is as(q) supposed to be?

Eq is not an explicit function of a symoblic variable, thus Eq(1) just calls to the first element of Eq, which corresponds to the equation you obtain.

Do you want to substitute the value of q=1 to Eq?

Nagulavancha Sai Preetham 2023-3-23

Yes, I want to substitute q = 1 in Eq. And as(q) is a redundant, so dont worry about it.

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Answer 1

Manikanta Aditya 2023-3-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1933820-how-to-convert-a-sym-data-type-to-symfun-datatype#answer_1198995

编辑：Manikanta Aditya 2023-3-23

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Hi Preetham,

As per my understanding, you are interested in finding the value of the expression. So, converting it to a function before finding the value gives the result.

Use the ‘symfun’ function on the required expression to convert it to a function.

syms as(q)
A = [1 2 3; 4 5 6; 7 8 9];
B = [2 3 4; 5 6 3; 9 9 10];
P = A - q*B;
Eq = symfun(det(P),q);
C=[3 4 5];
as(q) = 1;
disp(Eq(1));
as = as*poly2sym(C,q)*q;
disp(roots(sym2poly(Eq)));