How to use for loop when have syms inside the loop

Question

Sabella Huang 2022-5-30

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1730260-how-to-use-for-loop-when-have-syms-inside-the-loop

评论： Torsten 2022-5-31

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.

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Answer 1

Torsten 2022-5-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1730260-how-to-use-for-loop-when-have-syms-inside-the-loop#answer_974600

在 MATLAB Online 中打开

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

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Sabella Huang 2022-5-31

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 2022-5-31

在 MATLAB Online 中打开

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