The awgn function is implemented as a MATLAB function file in Communications Toolbox. If you have this toolbox installed, you can see the source code for this function.
You can call type to display it in the Command Window (which could display a lot of text in the Command Window, but offers no chance of accidentally modifying the function.)
You can call edit to open it in the MATLAB Editor (has no effect on the Command Window, but be careful not to modify it.)
You can call dbtype to display only certain sections of the text (displays less text in the Command Window but still offers no chance of accidentally modifying it.)
dbtype 1:10 awgn.m % Display just the first ten lines
Note that not all functions in MathWorks products are implemented as MATLAB function files (or MATLAB script files or MATLAB class files.) For something like the matrix multiplication operator (* or mtimes) it is implemented as a built-in function and we do not distribute the source code for built-in functions.
