How to convert a sym data type to symfun datatype?

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

[Sachin]

Could you please give more information about what you want ?

[Dyuman Joshi]

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]

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

Answer 1

[Manikanta Aditya]

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)));

For further reference, please refer to this link to know more about ‘symfun’ function:

• https://www.mathworks.com/help/symbolic/symfun.html

I hope this resolves your issue.