MATLAB: How to solve error in executing for loop due to Solve command used

for loopgraphplotqudratic equationsolve

angle=90;
theta=angle*pi/180;
m=cos(theta);
n=sin(theta);
%Sig1=Sigx*m^2+Sigy*n^2+2*m*n*Sigxy;
%Sig2=Sigx*n^2+Sigy*m^2-2*m*n*Sigxy;
%Sig6=Sigx*m*n+Sigy*n*m+(m*m-n*n)*Sigxy;
S1=1500;
S2=40;
S6=68;
for z=1:1500
    Sigx(z)=z;
    Sy=solve('(((z*m^2+Sigy*n^2)^2/(S1*S1))+((z*n^2+Sigy*m^2)^2/(S2*S2))+((z*m*n+Sigy*n*m)^2/(S6*S6))-(((z*m^2+Sigy*n^2)*(z*n^2+Sigy*m^2))/(S1*S1))=1)');
    Sigy(z)=Sy;
end
plot(Sigx, Sigy);
There is error in executing solve command….How to solve this?

Best Answer

Please note that when you use a quoted string as the argument to solve, then variables you have defined at the MATLAB level are not given those values for the purposes of solve(): they are treated as symbolic variables with unknown values. Then, because you have not indicated which of the symbolic variables to solve for, solve will try to solve for all of them and will fail because there are not enough equations to solve them simultaneously.
My guess at what you are trying to do is:
syms Sigy
for z=1:1500
    Sigx(z)=z;
    Sy(z) = solve( (((z*m^2+Sigy*n^2)^2/(S1*S1))+((z*n^2+Sigy*m^2)^2/(S2*S2))+((z*m*n+Sigy*n*m)^2/(S6*S6))-(((z*m^2+Sigy*n^2)*(z*n^2+Sigy*m^2))/(S1*S1))-1), Sigy);
end
Sigy = double(Sy);
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