Help with a Matrix for different angles

Greetings,

I am running the following code and I want to find out the value of sigma1, sigma2, and tau6 at each angle starting from 0. I was thinking of doing a for-lopp, but the problem is that I am not able to do negative thetas or 0.

I think the problem is that MatLAb is taking ALL the angles and creating one big solution based on all angles? i might be wrong here, but any help to achieve my goal would be greatly appreciated

theta=0:5:90;
m=cosd(theta);
n=sind(theta);

sigma1=sym('sigma_1');
sigma2=sym('sigma_2');
tau6=sym('tau_6');
stress=[sigma1; sigma2; tau6];

sigmax=0;
sigmay=0;
tau5=sym('taus');
stress_rotation=[sigmax; sigmay; tau5];

T=[m.^2  n.^2   2.*m.*n; 
   n.^2  m.^2  -2.*m.*n;
   -m.*n m.*n  m.^2-n.^2];

equation=stress==T.*stress_rotation;
solution=solve(equation, stress);
sigma1_f=vpa(solution.sigma_1);
sigma2_f=vpa(solution.sigma_2); 
tau6_f=vpa(solution.tau_6);

[John D'Errico]

There is no reason to post the same question twice.

[Eddy Ramirez]

wasnt sure if it went through the first time, but thank you for your feedback

[darova]

I see 4 uknowns but only 3 equations

[Eddy Ramirez]

yes - I want to get the values of sigma1, sigma2, and tau6 when i run the equation "stress==T.*stress_rotation" so for example when i run a 45* angle I get the following

Sigma1=taus

Sigma2=-taus

tau6=0

but when I run multiple angles, it does not work and I am not sure how to fix it

[darova]

Use for loop

[Eddy Ramirez]

Would the for loop allow me to run negative angles as well? I tried to do a for loop but it only allows me start with 1 through N.

[darova]

Try this way

ang = [-30 25 15];
for i = 1:length(ang)
    % code
end

[Eddy Ramirez]

yeah still no luck, i might have to recode it i just find it weird that a for loop doesnt do the trick. I wrote it as shown below but it does not work at all

theta=0:5:90;
m=cosd(theta);
n=sind(theta);
m2=m.^2;
n2=n.^2;

for i=1:length(theta)
    T=[m2(i)  n2(i)   2.*m(i).*n(i); 
       n2(i)  m2(i)  -2.*m(i).*n(i);
      -m(i)*n(i) m(i)*n(i)  m2(i)-n2(i)];
    
    sigma1=sym('sigma_1');
    sigma2=sym('sigma_2');
    tau6=sym('tau_6');
    stress=[sigma1; sigma2; tau6];

    sigmax=0;
    sigmay=0;
    tau5=sym('taus');
    stress_rotation=[sigmax; sigmay; tau5];
    
    equation=stress(i)==T.*stress_rotation(i);
    solution=solve(equation, stress);
    sigma1_f=vpa(solution.sigma_1);
    sigma2_f=vpa(solution.sigma_2); 
    tau6_f=vpa(solution.tau_6);
   
end

[Walter Roberson]

stress=[sigma1; sigma2; tau6];

That is a vector of length 3

equation=stress(i)==T.*stress_rotation(i);

but you index it at i where i can be up to length(theta)

Also your stress_rotation vector is length 3 as well.