how to create a data visualization with a function in Matlab

I am trying to study some codes inside a wireless communication textbook, which I have a piece of code from the textbook:

function PL=PL_free(fc,dist,Gt,Gr)
% Free Space Path loss Model
% Input
%       fc        : carrier frequency[Hz]
%       dist      : between base station and mobile station[m]
%       Gt        : transmitter gain
%       Gr        : receiver gain
% output
%       PL        : path loss[dB]
lamda = 3e8/fc;
tmp = lamda./(4*pi*dist);
if nargin>2
    tmp = tmp*sqrt(Gt); 
end
if nargin>3
    tmp = tmp*sqrt(Gr);  
end
PL = -20*log10(tmp);

And inside the textbook, there is also a graph that is generated based on this Matlab code. My question is, how can I create this graph based on the function myself? Do I need to have a data source for all of the variables? If I cannot get a data source like an excel file, is there any way inside Matlab there is a built-in tool that supports creating this graph? The graph is like this:
(I understand the concept of the plot which is in the command, enter some data of the function, but it will only show the answer of the function output. I cannot find a suitable solution anywhere online so here I come)

After revision:

I haven't testet this, but something along the lines of:

fc = __   % Choose value
Gt = __   % Choose value
Gr = __   % Choose value
dist = logspace(0, 3, 16);
PL=PL_free(fc,dist,Gt,Gr);
semilogx(dist, PL, 'ro')

Alternatively:

dist = logspace(0, 3, 16);
PL = zeros(1, numel(dist));
for ii = 1:numel(dist)
   PL(ii) = PL_free(fc, dist, Gt, Gr);
end
semilogx(dist, PL, 'ro')

I'm not sure if linspace or logspace is best here.linspace creates a vector with equally spaced values, while logspace creates a vector with logarithmically spaced values. To plot more values you can do hold on or hold all, and do semilogx with a new PL.