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

Question

Alexi 2021-12-11

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1608995-character-vectors-and-strings-in-the-first-argument-can-only-specify-a-variable-or-number

评论： Walter Roberson 2021-12-12

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

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?

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Answer 1

Walter Roberson 2021-12-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1608995-character-vectors-and-strings-in-the-first-argument-can-only-specify-a-variable-or-number#answer_853050

在 MATLAB Online 中打开

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))));

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Alexi 2021-12-12

unfortunately it didn't work like in past versions.

Walter Roberson 2021-12-12

在 MATLAB Online 中打开

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

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

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

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