How to use for loop when have syms inside the loop

Hello guys,

I want to ask about, how to use for loop when I have syms and diff inside looping. Here is my code that I tried to solve. Thank you

Xmax = 1410.34;

conc = [50 100 150]*1e-9;

ka = 3.46e3;

kd = 1.46e-4;

for i = 1:length(conc)

syms t x(t)

eqn = diff(x,t) == (ka*conc(:,i)*Xmax)-(ka*conc(:,i))*x-kd*x;

cond = x(0) == 0;

X_ass(t) = dsolve(eqn,cond);

X_ass = matlabFunction(X_ass);

t = linspace(0, 1800, 600)';

signal(:,i) = [X_ass(t)];

end

When I used this code, MATLAB give me warning this:

Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function

body must be sym expression.

Answer 1

[Torsten]

Try

syms t x(t)
Xmax = 1410.34;                                           
conc = [50 100 150]*1e-9;                    
ka   = 3.46e3; 
kd   = 1.46e-4; 
for i = 1:length(conc)
  eqn = diff(x,t) == (ka*conc(1,i)*Xmax)-(ka*conc(1,i))*x-kd*x;
  cond = x(0) == 0;
  X_ass(t) = dsolve(eqn,cond);
  X_ass = matlabFunction(X_ass);
  T  = linspace(0, 1800, 600)'; 
  signal(:,i) = X_ass(T);        
end

[Sabella Huang]

still cannot work sir. Its appear "Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym expression."

[Torsten]

Try

syms t x(t) c
Xmax = 1410.34;                                           
conc = [50 100 150]*1e-9;                    
ka   = 3.46e3; 
kd   = 1.46e-4; 
T  = linspace(0, 1800, 600)'; 
eqn = diff(x,t) == (ka*c*Xmax)-(ka*c)*x-kd*x;
cond = x(0)==0;
X_ass(t) = dsolve(eqn,cond);
for i = 1:numel(conc)
  X_ass_fun = matlabFunction(subs(X_ass,c,conc(i)));
  signal(:,i) = X_ass_fun(T);
end