Solution of system of linear equation
1 view (last 30 days)
Show older comments
Dear All I need to solve the system of linear equations. I have 5 variables [t0 rp V theta alpha]. I need to calculate V, theta, alpha from the following three equations at different known values of t0 and rp using solve command but the following message appears. Note : the first guess for t0=20e-3;rp=0.2e-2. "Error using solve (line 278) Input with 3 variables and output with 2 variables are inconsistent."
a = 0.45611;b1= 17.03;
q1 = 0.062988; q2 = 18.68;
c1 = 0.0026617;c2= -0.9238;
g=9.81; S=0.012;ro=1000;mw=5;rw=0.2e-3;m_bar=0.8;
syms V alpha theta
d1 =((1/2)*ro*V^2)*S*(a + b1*alpha^2);
Q = ((1/2)*ro*V^2)*S*(q1+q2*alpha);
T = ((1/2)*ro*V^2)*S*(c1 + c2*alpha);
eqn1 = -t0*g*sin(theta)+Q*alpha-d1 == 0;
eqn2 = t0*g*cos(theta)-Q-d1*alpha == 0;
eqn3 = T-m_bar*g*rp*cos(theta)==0;
eqns=[eqn1 eqn1 eqn3]
vars = [V alpha theta];
[solv, solu] = solve(eqns, vars)
1 Comment
John D'Errico
on 20 May 2018
Edited: John D'Errico
on 20 May 2018
Please learn to format your code next time to be readable.
https://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup#answer_18099
Answers (1)
John D'Errico
on 20 May 2018
Edited: John D'Errico
on 20 May 2018
First, why do you think this is a system of LINEAR equations?
theta is one of your unknowns. The presence of sin(theta) and cos(theta) would be enough to make that false. Then we have alpha and V. They appear in various forms, thus alpha, alpha^2, and V^2, and as a product of the two.
This is a system of NONLINEAR equations. The mere presence of an addition sign does not make them linear.
The error return is simple to understand. You have THREE unknowns, thus V, alpha, theta. You have TWO outputs: solv and solu. You provide no place to return THREE results. When called with one output, solve is smart enough to stuff the results as fields of a struct. But when you ask for three outputs and provide two containers it gets confused, and rightfully so.
3 Comments
See Also
Categories
Find more on Equation Solving 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!