Combining two equations in S domain

Hey fellas, Simple problem here, but I can't seem to figure it. I'm trying to write two equations and combine the two before plotting the resulting time function.

For the first element:

w0 = 1;      %rad/s%
zeta = 0.15; %damping ratio%
wn = (w0)/((1-(zeta^2))^(1/2));
R = 1;
num = (wn^2);
den = [1 (2*zeta*wn) (wn^2)];
Ideal = tf(num,den);
t=0:0.1:30;
step(R*Ideal,t);
axis([0 30 0 2]);
stepinfo(Ideal)

This strip will result in a plotted step response of a transfer function in the S domain. If my other equation is in the time domain, one must 'laplace' yes?

a = 0;
b = 1;
c = 6;
T = 0.1;
% Conversion to 'sym' from 'tf' is not possible.
G = a+(b./(1+exp(c*(T-t))));
S = laplace(G);
Y = S*Ideal;
y = ilaplace(Y);

With all input variables given except 't', one would think it's a simple matter to just laplace it and multiply the two in the S domain before ilplace back, but I've encountered three errors, each at different points:

Undefined function 'laplace' for input arguments of type 'double'.
Undefined function 'transform' for input arguments of type 'char'.

and, if we 'which laplace -all' and enter the function manually, we get

Error in laplace (line 28)
L = transform('laplace', 't', 's', 'z', F, varargin{:});

Eventually I want to plot the resulting function between these two; is there any insight on this issue?

Answer 1

[Walter Roberson]

https://www.mathworks.com/matlabcentral/fileexchange/10816-mimo-toolbox has tf2sym and sym2tf to allow you to convert the tf (transfer function) to symbolic, as laplace and ilaplace are defined on symbolic.

[Michael Dupre]

I already had an external function to deal with the tf(transfer function) to symbolic, so that's not the issue :)

[Walter Roberson]

At the point

 G = a+(b./(1+exp(c*(T-t))));

you should be using symbolic t rather than numeric t.