solve equation without fsolve
3 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
Hello,
I have the following equation that I'm trying to solve. I need to solve for T for a very long array of known RT
function RT=RTD(T)
a=0.003925;
b=0.110361;
d=1.492690;
R0=100;
RT=R0*(1+a*(1+d/100)*T-a*d/100^2*T^2+a*b/100^3*T^3-a*b/100^4*T^4);
I dont think I have fsolve or symbolic toolbox installed. Is there anyway to automate this without using those?
Thanks
0 commentaires
Réponses (3)
Naz
le 19 Oct 2011
Assuming that each RT will yield four roots:
a=0.003925;
b=0.110361;
d=1.492690;
R0=100;
T=zeros(4,length(RT));
for n=1:length(RT)
T(:,n)=roots(-a*b/100^4*R0 a*b/100^3*R0 -a*d/100^2*R0 a*(1+d/100)*R0 (1-RT(n))*R0);
end
If you want to create an actual function, go to file->new->script and paste the following:
function [T]=RTD(RT)
a=0.003925;
b=0.110361;
d=1.492690;
R0=100;
T=zeros(4,length(RT));
for n=1:length(RT)
T(:,n)=roots(-a*b/100^4*R0 a*b/100^3*R0 -a*d/100^2*R0 a*(1+d/100)*R0 (1-RT(n))*R0);
end
end
Then you can call this function and pass your array of RT. The function will return you an array of T.
T=RTD(RT)
P.S. Make sure there is enough parenthesis in the equation so the coefficients are calculated properly. I recommend to calculate the coefficients prior sending them to roots function. This also will save some time, since the coefficients will be calculated only once instead of each loop.
1 commentaire
Walter Roberson
le 19 Oct 2011
You left out the [] in that roots() call, so this code will end up taking roots() of a scalar.
Andrei Bobrov
le 19 Oct 2011
a=0.003925;
b=0.110361;
d=1.492690;
R0=100;
syms k T
cf = coeffs(k-R0*(1+a*(1+d/100)*T-a*d/100^2*T^2+a*b/100^3*T^3-a*b/100^4*T^4),T)
fcf = matlabFunction(cf(end:-1:1))
RTD = @(RT)cell2mat(arrayfun(@(x)roots(fcf(x)),RT,'un',0))
use function RTD
T = RTD(RT)
1 commentaire
Valerio
le 18 Juil 2013
I have used your proposed solution, but the output variable of Temp = RTD(RT) is the sym T. What is the problem? Can you help me?
Thanks
Walter Roberson
le 18 Oct 2011
roots( [R0*a*b, -100*R0*a*b, 10000*R0*a*d, -100000000*R0*a-1000000*R0*a*d, -100000000*R0+100000000*RT] )
Note that roots() can only process one set of coefficients at a time: it is not vectorized.
0 commentaires
Voir également
Catégories
En savoir plus sur Calculus dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!