Error in sym/subref

%Indicate variables
x0 =1.25;
S0 =86.63;
P0 =0;
Kd = 0.0032;
a = 0.6212;
Yps = 0.5820;
Ki = 243.95;
c = 0.5557; 
Ks = 0.0191;
d = 30.7600; 
syms t S
mu = ((c*S)/Ks+S+(S^2/Ki))*(1-(-Yps*S+Yps*S0+P0/d));
m1 = exp(int(mu,0,t));
m2 = (-a*c/Yps)*((S+Yps*S^2-Yps*S*S0-P0*S)/Ks+S+(S^2/Ki));

%% 1st method ODE
x=linspace(0,0.5,50);
h=0.5;
f1= 86.63;
for i = 1:length(x)
    f(i+1) = f(i) + h*(m1(i)*m2(i));
end

Index exceeds the number of array elements (1).

Error in sym/subsref (line 900)

R_tilde = builtin('subsref',L_tilde,Idx);

Answer 1

[Walter Roberson]

m1 and m2 are scalar symbolic expressions that do not involve x.

They do involve S. perhaps you want to subs(m1, S, x(i)) ?