Whenever I type in syms x and run it, Matlab seems like it's being looped and I also can't stop it. How do I fix it?

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Khôi Nam Nguyen 2018-5-5

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https://ww2.mathworks.cn/matlabcentral/answers/399235-whenever-i-type-in-syms-x-and-run-it-matlab-seems-like-it-s-being-looped-and-i-also-can-t-stop-it

评论： GAGANDEEP KAUR 2020-11-5

I always need to use task manager to stop Matlab because pressing X doesn't shut it down.The problem just started today and I don't now why it keeps happening.

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Steven Lord 2018-5-5

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https://ww2.mathworks.cn/matlabcentral/answers/399235-whenever-i-type-in-syms-x-and-run-it-matlab-seems-like-it-s-being-looped-and-i-also-can-t-stop-it#answer_318834

Are you using Windows 10 Spring Creator Update 2018? If so see Bug Report 1755918.

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GAGANDEEP KAUR 2020-11-3

编辑：Walter Roberson 2020-11-4

在 MATLAB Online 中打开

I have updated the version for R2018a but is still hving issue with the syms command , keep on running the code and not showing any result.Please if I could get some help

Here is the section I am having trouble with

syms a b c d e;
K1=zeros(1,5);K2=zeros(1,5);K3=zeros(1,5);K4=zeros(1,5);K5=zeros(1,5);
 for i=1:9
%calculating  mole fractions of ionic species
x1=[0.5096 0.5092 0.5087 0.4852 0.4847 0.4834 0.4804 0.4805 0.4803];
x2=[0.0963 0.0964 0.0965 0.1163 0.1161 0.1158 0.1275 0.1266 0.1253];
x3=[0.3941 0.3944 0.3948 0.3985 0.3992 0.4008 0.3921 0.3929 0.3943];   
T=[394.15 399.15 404.15 375.15 390.15 405.15 374.15 392.15 406.15]; 
%Equilibrium constant for reaction 1 (Solvation reaction)
K1(i)=exp((-8.549)+(6692/T(i)))
%Equilibrium constant for reaction 2(Ionization of water)
K2(i)=100
%Equilibrium constant for reaction 3(Dissociation of HI)
K3(i)=exp((16.93565)+((1250)/T(i))+(-2.575*log(T(i))))
%Equilibrium constant for reaction 4(Polyiodide formation a)
K4(i)=exp((-936.28)+((40216.27)/T(i))+(151.983*(log(T(i))))+(-0.1675*(T(i))))
%Equilibrium constant for reaction 5(Polyiodide formation b)
K5(i)=exp((1044.78)+(-45171.42/T(i))+(-165.20*log(T(i)))+(0.1511*(T(i))))
eqns=[((d*(c-e))/((x1(i)-a-b-c-d)^5)*(x2(i)-d-b-c))==K1(i),((a+b+c)*a)/((x1(i)-a-b-c-d)^2)==K2(i),((a+b+c)*(d+b))/((x1(i)-a-b-c-d)*(x2(i)-d-b-c-e))==K3(i),((a+b+c)*(c-e))/((x1(i)-a-b-c-d)^4*(x2(i)-d-b-c-e))==K4(i), (((e)*(x1(i)-a-b-c-d)^3)/((c-e)*(x3(i)-e)))==K5(i)];
S=solve(eqns,[a,b,c,d,e]);
S.a(S.a<0)=[];
S.b(S.b<0)=[];
S.c(S.c<0)=[];
S.d(S.d<0)=[];
S.e(S.e<0)=[];
S.a=double(S.a)
S.b=double(S.b)
S.c=double(S.c)
S.d=double(S.d)
S.e=double(S.e)
end

Walter Roberson 2020-11-4

在 MATLAB Online 中打开

You should re-arrange.

... It will not help... but you should re-arrange.

syms a b c d e;
x1=[0.5096 0.5092 0.5087 0.4852 0.4847 0.4834 0.4804 0.4805 0.4803];
x2=[0.0963 0.0964 0.0965 0.1163 0.1161 0.1158 0.1275 0.1266 0.1253];
x3=[0.3941 0.3944 0.3948 0.3985 0.3992 0.4008 0.3921 0.3929 0.3943];   
T=[394.15 399.15 404.15 375.15 390.15 405.15 374.15 392.15 406.15];
N = length(x1);
K1 = zeros(1,N);
K2 = zeros(1,5);
K3 = zeros(1,N);
K4 = zeros(1,N);
K5 = zeros(1,N);
Sout = struct();
 for i=1:N
%calculating  mole fractions of ionic species
%Equilibrium constant for reaction 1 (Solvation reaction)
K1(i)=exp((-8.549)+(6692/T(i)));
%Equilibrium constant for reaction 2(Ionization of water)
K2(i)=100;
%Equilibrium constant for reaction 3(Dissociation of HI)
K3(i)=exp((16.93565)+((1250)/T(i))+(-2.575*log(T(i))));
%Equilibrium constant for reaction 4(Polyiodide formation a)
K4(i)=exp((-936.28)+((40216.27)/T(i))+(151.983*(log(T(i))))+(-0.1675*(T(i))));
%Equilibrium constant for reaction 5(Polyiodide formation b)
K5(i)=exp((1044.78)+(-45171.42/T(i))+(-165.20*log(T(i)))+(0.1511*(T(i))));
eqns=[((d*(c-e))/((x1(i)-a-b-c-d)^5)*(x2(i)-d-b-c))==K1(i),((a+b+c)*a)/((x1(i)-a-b-c-d)^2)==K2(i),((a+b+c)*(d+b))/((x1(i)-a-b-c-d)*(x2(i)-d-b-c-e))==K3(i),((a+b+c)*(c-e))/((x1(i)-a-b-c-d)^4*(x2(i)-d-b-c-e))==K4(i), (((e)*(x1(i)-a-b-c-d)^3)/((c-e)*(x3(i)-e)))==K5(i)];
S=vpasolve(eqns,[a,b,c,d,e]);
mask = S.a < 0 | S.b < 0 | S.c < 0 | S.d < 0 | S.e < 0;
S.a(mask)=[];
S.b(mask)=[];
S.c(mask)=[];
S.d(mask)=[];
S.e(mask)=[];
Sout(i).a=double(S.a);
Sout(i).b=double(S.b);
Sout(i).c=double(S.c);
Sout(i).d=double(S.d);
Sout(i).e=double(S.e);
disp(Sout(i))
end

Walter Roberson 2020-11-4

That is the expected message when you control-c to stop execution.

vpasolve is either not able to find an answer or takes a very long time to find an answer even when I tell it to start at a position that is pretty close to working (but not quite working.) My searches have not found any solution when I confine the values to +/- 1e6. And definitely not positive values only.

By the way, the equations have a singularity when c==e, leading to +/- infinity.

GAGANDEEP KAUR 2020-11-5