Evaluate values of a vector with values of variable p

Question

ABG 2022-10-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1833263-evaluate-values-of-a-vector-with-values-of-variable-p

评论： ABG 2022-10-23

Hi guys!

I am having a bit of a problem with a code. In this case I have calculated values of exx and eyy, which depend on p. After having computed this two vectors, I want to obtain the values of vector uc which depends on the values of exx and eyy related with the particular value of p.

However, when I try to substitute all the exx and eyy values into uc, I do not obtain the correct substitution as I am only obtaining the same result, which also keeps depending on p (I do not know why if I am giving p values to the two previous vectors). I do not know if I have to do it with another FOR value, which allows me to store a certain value of p and pair it to the values of exx and eyy.

Thanks a lot!

syms E ex ey r v t p
Pa=(E*ex)/((r/2*t)-v*r/t);
Po=(E*ey)/(-v*(r/2*t)+r/t);
%Value of all derivatives
%Calculation of the derivatives
dPa1=diff(Pa,E);
dPa2=diff(Pa,ex);
dPa3=diff(Pa,r);
dPa4=diff(Pa,v);
dPa5=diff(Pa,t);
dPo1=diff(Po,E);
dPo2=diff(Po,ey);
dPo3=diff(Po,r);
dPo4=diff(Po,v);
dPo5=diff(Po,t);
%Values of u
u1=sqrt((0.05*70*10^3)^2/3); % u for E coefficient
u2=sqrt((0.05*0.3)^2/3); % u for v Poisson's coefficient
u3=sqrt(1^2/3); % u for r
u4=sqrt(0.01^2/3); % u for t
u5=sqrt((5*10^-6)^2/3); % u for strain
%Now we give values to all the variables
E=70*10^3;
v=0.3;
r=33;
t=0.1;
exx=[];
eyy=[];
ex=(((p*r)/(2*t))-v*((p*r)/t))*1/E;
ey=(-v*((p*r)/(2*t))+((p*r)/t))*1/E;
uc=[];
ucc=[];
for p=0:0.001:0.2
   exx=[exx eval(ex)];
   eyy=[eyy eval(ey)];
   uc=[uc sqrt((eval(dPa1)*u1)^2+(eval(dPa2)*u2)^2+(eval(dPa3)*u3)^2+(eval(dPa4)*u4)^2+(eval(dPa5)*u5)^2+(eval(dPo1)*u1)^2+(eval(dPo2)*u2)^2+(eval(dPo3)*u3)^2+(eval(dPo4)*u4)^2+(eval(dPo5)*u5)^2)]; %uc in terms of p
end

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Answer 1

Walter Roberson 2022-10-23

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https://ww2.mathworks.cn/matlabcentral/answers/1833263-evaluate-values-of-a-vector-with-values-of-variable-p#answer_1081518

eval() of a symbolic expression is not defined. Use subs() and double()

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Walter Roberson 2022-10-23

eval() of a symbolic expression is in practice eval of char() of the expression. See https://www.mathworks.com/matlabcentral/answers/1833228-import-a-symbolic-expression-to-simulink-and-plot-it#answer_1081478 for why that does not work.

ABG 2022-10-23