complicated system of 3 equations,3 unknowns

Question

Faraz Vossoughian 2017-12-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/371089-complicated-system-of-3-equations-3-unknowns

编辑： Roger Stafford 2017-12-5

I'm trying to solve a big system of 3 equations 3 unknowns, but i keep getting 0 for all three variables which i'm certain is wrong. I was wondering if im doing something wrong.alph1 alph2 alph3 are my equations and A1 A3 A5 are unknown. Please help me

syms A1 A3 A5 b cr ct
clc
AR=8;
lamda=0.4;
an=2*pi;
zerolift=deg2rad(-1.5);
angleofa=deg2rad(7.6);
teta=[pi/6,pi/3,pi/2];
lamda=0.4;
ct=lamda*cr;
eqn=(b^2)/((cr+ct)*(b/2))==AR;
b=solve(eqn,b);
y1=(-b/2)*cos(teta(1));
y2=(-b/2)*cos(teta(2));
y3=(-b/2)*cos(teta(3));
c1=-cr*((3*3^(1/2))/10 - 1);
c2=cr*(1+(1-lamda)*((2*y2)/b));
c3=cr*(1+(1-lamda)*((2*y3)/b));
n=1
alph1=((2*b)/(pi*c1))*((A1*sin(teta(n)))+(A3*sin(3*teta(n)))+(A5*sin(5*teta(n))))+zerolift+((1*A1*(sin(1*teta(n))/sin(teta(n))))+(3*A3*(sin(3*teta(n))/sin(teta(n))))+(5*A5*(sin(5*teta(n))/sin(teta(n)))));
n=2
alph2=((2*b)/(pi*c2))*((A1*sin(teta(n)))+(A3*sin(3*teta(n)))+(A5*sin(5*teta(n))))+zerolift+((1*A1*(sin(1*teta(n))/sin(teta(n))))+(3*A3*(sin(3*teta(n))/sin(teta(n))))+(5*A5*(sin(5*teta(n))/sin(teta(n)))));
n=3
alph3=((2*b)/(pi*c3))*((A1*sin(teta(n)))+(A3*sin(3*teta(n)))+(A5*sin(5*teta(n))))+zerolift+((1*A1*(sin(1*teta(n))/sin(teta(n))))+(3*A3*(sin(3*teta(n))/sin(teta(n))))+(5*A5*(sin(5*teta(n))/sin(teta(n)))));
eqn1=alph1==zerolift;
eqn2=alph2==zerolift;
eqn3=alph3==zerolift;
sol=solve([eqn1,eqn2,eqn3],[A1,A3,A5]);
A1=sol.A1;
A3=sol.A3;
A5=sol.A5;

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Star Strider 2017-12-5

I edited your Question to select your code, and used the [{}Code] button to format it correctly.

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Answer 1

Roger Stafford 2017-12-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/371089-complicated-system-of-3-equations-3-unknowns#answer_294712

编辑：Roger Stafford 2017-12-5

You have included 'zerolift' in the alpha equations, but in the 'eqn' equations you have also set the expressions to 'zerolift' which cancels it out. Hence, all zeros would be the solution. You should be consistent. Either include it in the alpha's or include it in the equ's, but not both.