Note: I actually gave the input as -1 as an initial guess. The actual solution via vpasolve() is -.6....
fsolve giving error that solution is not finite and real. When I test using vpasolve() I get a solution, then I input the same solution and get same error of not finite/real.
1 view (last 30 days)
Show older comments
c1 = 0.5176;
c2 = 116;
c3 = .4;
c4 = 0.4;
c5 = 5;
c6 =21;
c7 = .08;
c8 = .035;
syms lambda
for k = 1:600
theta = pitch.Data(k);
%cp(k) = c1*(c2/lambda - c3*theta -c5)*exp(c6/lambda);
cp(k) = c1*(c6*lambda + (-c4 - c3*(2.5 + theta) + c2*(1/(lambda + ...
c7*(2.5 + theta)) - c8/(1 + (2.5 + theta)^3)))/exp(c5*(1/(lambda + ...
c7*(2.5 + theta)) - c8/(1 + (2.5 + theta)^3))));
eqn(k) = cp(k)/(2*lambda^3) == 1e7*(ta_kf.Data(k))/(rho*pi*N^5*wr_kf.Data(k)^2);
tsr(k) = vpasolve(eqn(k),lambda);%
tsr_check(k) = fzero(@(lambda)cp(k),[-1 0]);
end
Answers (1)
Torsten
on 13 Jun 2022
c1 = 0.5176;
c2 = 116;
c3 = .4;
c4 = 0.4;
c5 = 5;
c6 =21;
c7 = .08;
c8 = .035;
syms lambda
for k = 1:600
theta = pitch.Data(k);
%cp(k) = c1*(c2/lambda - c3*theta -c5)*exp(c6/lambda);
cp(k) = c1*(c6*lambda + (-c4 - c3*(2.5 + theta) + c2*(1/(lambda + ...
c7*(2.5 + theta)) - c8/(1 + (2.5 + theta)^3)))/exp(c5*(1/(lambda + ...
c7*(2.5 + theta)) - c8/(1 + (2.5 + theta)^3))));
eqn(k) = cp(k)/(2*lambda^3) == 1e7*(ta_kf.Data(k))/(rho*pi*N^5*wr_kf.Data(k)^2);
tsr(k) = vpasolve(eqn(k),lambda);%
expr = cp(k)/(2*lambda^3) - 1e7*(ta_kf.Data(k))/(rho*pi*N^5*wr_kf.Data(k)^2);
fun = matlabFunction(expr,'Vars',lambda);
tsr_check(k) = fzero(fun,[-1 0]);
end
8 Comments
Torsten
on 13 Jun 2022
@Gordon comment moved here:
fsolve() is not a good enough solver in this situation because of the rate of change of the data. Therefore, vpasolve() needed to be used. The reason for trying to implement fsolve is because simulink does not allow vpasolve() a solution therefore is to use code.extrinsic() to implement function including vpasolve().
Torsten
on 13 Jun 2022
Edited: Torsten
on 13 Jun 2022
If the solution for index k is "near" to the solution of index k-1, it is usually a good idea to take the solution of step k-1 as initial guess for the solution of index k. Something like
c1 = 0.5176;
c2 = 116;
c3 = .4;
c4 = 0.4;
c5 = 5;
c6 =21;
c7 = .08;
c8 = .035;
tsr_guess = 1.0;
syms lambda
for k = 1:600
theta = pitch.Data(k);
%cp(k) = c1*(c2/lambda - c3*theta -c5)*exp(c6/lambda);
cp(k) = c1*(c6*lambda + (-c4 - c3*(2.5 + theta) + c2*(1/(lambda + ...
c7*(2.5 + theta)) - c8/(1 + (2.5 + theta)^3)))/exp(c5*(1/(lambda + ...
c7*(2.5 + theta)) - c8/(1 + (2.5 + theta)^3))));
eqn(k) = cp(k)/(2*lambda^3) == 1e7*(ta_kf.Data(k))/(rho*pi*N^5*wr_kf.Data(k)^2);
tsr(k) = vpasolve(eqn(k),lambda);%
expr = cp(k)/(2*lambda^3) - 1e7*(ta_kf.Data(k))/(rho*pi*N^5*wr_kf.Data(k)^2);
fun = matlabFunction(expr,'Vars',lambda);
tsr_check(k) = fsolve(fun,tsr_guess);
tsr_guess = tsr_check(k);
end
See Also
Categories
Find more on Calculus in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!