What should be done?
I'm afraid the answer is: learn matlab. Function inputs are variables. Matlab is not going to magically guess that a particular variable should suddenly get its content from a file that has (parts) of its name identical to a variable name.
Now, you could create your function where the input variable contains the name of the file to load:
function [edges, nodes, path] = PRM(obstaclefilename)
which you script could call with:
folder = 'C:\somewhere\somefolder';
filename = 'obstacle.csv';
[edges, nodes, path] = PRM(fullfile(folder, filename));
The body of the function could start with:
function [edges, nodes, path] = PRM(obstaclefilename)
filecontent = readtable(obstaclefilename); %use readtable or some other file import function
%... rest of the code that uses filecontent
end
