Indexing Error Using 'dsolve'

I'm trying to write a script to solve the differential equation and then display the solution with a few different initial conditions.

This is the code so far:

syms t k1 k2 M A0 A
% Differential equation
dA_dt = 1 * (20 - A) - 3 * A;
% Solving for A(t) with different initial conditions
A_sol_0 = dsolve(dA_dt, A(0) == 1);
A_sol_2 = dsolve(dA_dt, A(0) == 2);
A_sol_5 = dsolve(dA_dt, A(0) == 5);
A_sol_10 = dsolve(dA_dt, A(0) == 10);
% Displaying the solutions
disp('Solution for A0 = 0:');
disp(A_sol_0);
disp('Solution for A0 = 2:');
disp(A_sol_2);
disp('Solution for A0 = 5:');
disp(A_sol_5);
disp('Solution for A0 = 10:');
disp(A_sol_10);

And the error I keep getting is:

Array indices must be positive integers or

logical values.

Error in indexing (line 968)

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

Error in ************ (line 7)

A_sol_0 = dsolve(dA_dt, A(0) == 1);

Help would be GREATLY appreciated.

Answer 1

[VBBV]

syms t k1 k2 M A0 A(t) 

dA_dt = 1 * (20 - A) - 3 * diff(A,t) == 0;
% Solving for A(t) with different initial conditions
A_sol_0 = dsolve(dA_dt, A(0) == 0);
A_sol_2 = dsolve(dA_dt, A(0) == 2);
A_sol_5 = dsolve(dA_dt, A(0) == 5);
A_sol_10 = dsolve(dA_dt, A(0) == 10);
% Displaying the solutions
disp('Solution for A0 = 0:');

Solution for A0 = 0:

disp(A_sol_0);

disp('Solution for A0 = 2:');

Solution for A0 = 2:

disp(A_sol_2);

disp('Solution for A0 = 5:');

Solution for A0 = 5:

disp(A_sol_5);

disp('Solution for A0 = 10:');

Solution for A0 = 10:

disp(A_sol_10);

[VBBV]

dA_dt = 1 * (20 - A) - 3 * A;% this is not a differential equation