Character vectors and strings in the first argument can only specify a variable or number.

Character vectors and strings in the first argument can only specify a variable or number.

To evaluate character vectors and strings representing symbolic expressions, use str2sym

Tmr=3728;
Amr=932;
rho=0.002378;
Ohm=36;
Rmr=17.22;
smr=0.034;
Cla_d=0.11;
Cla_r=Cla_d/0.01745;
a=1131.55;  
bmr=2;
CTreq=Tmr/(rho*Amr*(Ohm*Rmr)^2);
tetatwdeg=-12;
tetatwrad=tetatwdeg*0.01745;
for i=1:1:12
    if i==1
        teta0rad=(6*CTreq/(smr*Cla_r))-(0.75*tetatwrad+(0.75*sqrt(2)*sqrt(CTreq)));
    else
        teta0rad=(6*CTreq/(smr*Cla_r))-(0.75*tetatwrad+(1.5*sqrt(CTreq/2)));
    end
    myEqn = sym('teta0rad =(6*CT/(smr*Cla_r))-(0.75*tetatwrad+(1.5*sqrt(CT/2)))');
    newEqn = subs(myEqn,{'teta0rad','smr','Cla_r','tetatwrad'}, [teta0rad,smr,Cla_r,tetatwrad]);
    CTi=solve(newEqn); 
    teta0rad=teta0rad+(6*(CTreq-CTi)/(smr*Cla_r))+(0.75*sqrt(2)*(sqrt(CTreq)-sqrt(CTi)));
end

Why do I get that error?

Answer 1

[Walter Roberson]

change

myEqn = sym('teta0rad =(6*CT/(smr*Cla_r))-(0.75*tetatwrad+(1.5*sqrt(CT/2)))');
newEqn = subs(myEqn,{'teta0rad','smr','Cla_r','tetatwrad'}, [teta0rad,smr,Cla_r,tetatwrad]);

to

syms CT
newEqn = teta0rad == (6*CT/(smr*Cla_r))-(0.75*tetatwrad+(1.5*sqrt(CT/2))));

[Steven Lord]

The reason why you need to do this is because of the second entry in the Compatibility Considerations section on the documentation page for the sym function.

[Alexi]

unfortunately it didn't work like in past versions.

[Walter Roberson]

Tmr=3728;
Amr=932;
rho=0.002378;
Ohm=36;
Rmr=17.22;
smr=0.034;
Cla_d=0.11;
Cla_r=Cla_d/0.01745;
a=1131.55;  
bmr=2;
CTreq=Tmr/(rho*Amr*(Ohm*Rmr)^2);
tetatwdeg=-12;
tetatwrad=tetatwdeg*0.01745;
for i=1:1:12
    if i==1
        teta0rad=(6*CTreq/(smr*Cla_r))-(0.75*tetatwrad+(0.75*sqrt(2)*sqrt(CTreq)));
    else
        teta0rad=(6*CTreq/(smr*Cla_r))-(0.75*tetatwrad+(1.5*sqrt(CTreq/2)));
    end
    syms CT
    newEqn = teta0rad == (6*CT/(smr*Cla_r))-(0.75*tetatwrad+(1.5*sqrt(CT/2)));
    CTi=solve(newEqn); 
    teta0rad=teta0rad+(6*(CTreq-CTi)/(smr*Cla_r))+(0.75*sqrt(2)*(sqrt(CTreq)-sqrt(CTi)));
end
simplify(teta0rad)

ans = 

double(teta0rad)

ans = 0.2094