Symbolic toolbox substitution causing large values

I am creating a Jacobian matrix for a state space model. I Delcared all the constants and variables as variables in syms. After Jacobian when i substitue the constant values I getting some values which are not the exact values what i want. Can any help me in this?

clc
clear all
syms v T m qa Ta mg tow cv R Va B0 a A0 B C0 c Tg gamma
f1 = qa
f2 = ((Ta-T)/tow)-(T/cv)*(qa/m)*{(R*mg*(1+mg.^2/Va.^2)/Va)+(mg.^2/Va.^2)*(B0*R+2*C0/Tg.^3)-...
    ((2*c*mg.^3/Va.^3*Tg.^3)*(1+gamma*mg.^2/Va.^2)*exp(-gamma*mg.^2/Va.^2))}
f3 = 0
%to solve the variabes
j = jacobian([f1 f2 f3],[v T m])
var = subs(j,[B0,C0,R,Tg,Va,c,cv,gamma,mg,tow],[4.07*10.^-5,816.58,8.134,295,25*10.^-3,0.07381,20.8040,5.3*10.^-9,144.1832,26.574])

Answer 1

[John D'Errico]

A REALLY bad idea is to name your variables things like var, as that is also the name of a terribly useful function.

So your next question will be why does the function var no longer work anymore.

syms v T m qa Ta mg tow cv R Va B0 a A0 B C0 c Tg gamma
f1 = qa

f1 = 

qa

f2 = ((Ta-T)/tow)-(T/cv)*(qa/m)*{(R*mg*(1+mg.^2/Va.^2)/Va)+(mg.^2/Va.^2)*(B0*R+2*C0/Tg.^3)-...
    ((2*c*mg.^3/Va.^3*Tg.^3)*(1+gamma*mg.^2/Va.^2)*exp(-gamma*mg.^2/Va.^2))}

f2 = 

f3 = 0

f3 = 0

%to solve the variabes
j = jacobian([f1 f2 f3],[v T m])

j = 

var = subs(j,[B0,C0,R,Tg,Va,c,cv,gamma,mg,tow],[4.07*10.^-5,816.58,8.134,295,25*10.^-3,0.07381,20.8040,5.3*10.^-9,144.1832,26.574])

var = 

vpa(var,5)

ans = 

I don't see anything big. Perhaps you don't know about vpa, to convert those numbers into floating point results?

[Siva P M]

yes i got the answer thank you very much. I was not aware of vpa.