Error in assigning value to variable while solving non-linear equations using syms

I am trying to solve some non-linear equations. While running I am getting error as follows. May I please know what exactly this error means( as I need min positive value from all the solutions) and it can be resolved

Unable to perform assignment because the left and right sides have a different number of elements.

Error in SpeciationCal (line 29)

n(i)=min(S.b)

syms a b c

x3=[0.000804557 0.038813753 0.109515494 0.258253623 0.250365943 0.266695352 0.254064153 0.355464596 0.367390937 0.367899743];

x1=[0.812965986 0.75197909 0.647030256 0.315659359 0.381316826 0.324185571 0.385450182 0.198472313 0.161364552 0.181784492];

x2=[0.186229457 0.209207157 0.243454249 0.426087018 0.368317231 0.409119077 0.360485665 0.446063091 0.47124451 0.450315765];

T=[384.2 392.1 396.4 392 406.1 405 409.6 416.2 416.4 417.1];

N=length(x1);

K1=zeros(N,1);K2=zeros(N,1);K3=zeros(N,1);m=zeros(N,1);n=zeros(N,1);o=zeros(N,1);

for i=1:N

K1(i)=exp((-936.28)+((40216.27)/T(i))+(151.983*(log(T(i))))+(-0.1675*(T(i))))

K2(i)=exp((1044.78)+(-45171.42/T(i))+(-165.20*log(T(i))+(0.1511*(T(i)))))

K3(i)=exp((-228.838)+(12587.48/T(i))+(40.68593*log(T(i)))+(-0.09838*(T(i))))

eqns=[((a*(a-b))/((x1(i)-a-c+3*b)*(x2(i)-a-c)))==K1(i),((b*3*b)/(a-b)*(x3(i)-b))==K2(i),((c*c)/((x1(i)-a-c+3*b)*(x2(i)-a-c)))==K3(i)]

S=vpasolve(eqns,[a,b,c])

warning('off', 'symbolic:numeric:NumericalInstability')

S.a(S.a<0)=[];

S.b(S.b<0)=[];

S.c(S.c<0)=[];

idxa= abs(imag(S.a)) < eps;

idxb = abs(imag(S.b)) < eps;

idxc = abs(imag(S.c)) < eps;

S.a = S.a(idxa);

S.b = S.b(idxb);

S.c = S.c(idxc);

m(i)=min(S.a)

n(i)=min(S.b)

o(i)=min(S.c)

end