plotting ode warning with nor plot returned

Trying to plot both of these ODEs against each other.

he error that is being returned is.

Warning: Error updating ParameterizedFunctionLine.

 The following error was reported evaluating the function in FunctionLine update: Unable to convert expression into double array.
 

and the code is.

syms A(t) B(t) 
N = 1000;
gamma = 0.1;
beta = 0.95;

eqns = [diff(A,t) == -beta*(B/N)*A+gamma*B, diff(B,t) == beta*(B/N)*(N-B)-gamma*B];
S = dsolve(eqns);
fplot(A,B)

Answer 1

[Star Strider]

It helps to look at the dsolve results:

Bsol = S.B
Asol = S.A

that are:

Bsol =
                                     0
                              17000/19
 -17000/(19*(exp(C1 - (17*t)/20) - 1))
 
Asol =
                                              C3
 exp(-(17*t)/20)*(C2 + (2000*exp((17*t)/20))/19)
    2000/19 - C4/(19*(exp((17*t)/20) - exp(C1)))

Provide numerical values for the initial conditions ‘C1’ and ‘C2’ and the rest, and the plot should magically appear!

Answer 2

[Walter Roberson]

You dsolve() and store the answer but then you try to fplot the unprocessed A and B. At the very least you would want to plot S.A and S.B

However you would need to add boundary conditions in order to get S.A and S.B in a form that you can plot.