why does the command window show 'Unrecognized function or variable 'beta_est'.'? how to solve it?

Question

Haotian Wang 2021-5-5

编辑： KSSV 2021-5-5

syms bets_est;
for t=1:n-1;
    func=(sigma2(t+1)-sigma2(t))/(S(t+1)-S(t))*S(t)/sigma2(t)==beta_est(t)-2;
end
solve(eq,beta_est);

where sigma2 is an anrray with 1*809, S is an anrray with 1*809,n=809.

I would like to solve this equation. And here is what the command window shows.

>> for t=1:n-1;
    func=(sigma2(t+1)-sigma2(t))/(S(t+1)-S(t))*S(t)/sigma2(t)==beta_est(t)-2;
end
Unrecognized function or variable 'beta_est'.

Answer 1

KSSV 2021-5-5

编辑：KSSV 2021-5-5

Replace the line:

syms bets_est;

with

syms beta_est;

By the way you need not to use syms.

You can straight away solve using:

beta_est(t) = (sigma2(t+1)-sigma2(t))/(S(t+1)-S(t))*S(t)/sigma2(t) +2;

No loop needed... use

beta_est = diff(sigma2)./(diff(S)).*S(1:end-1)./sigma2(1:end-1) +2;