function A=function_filename(c,d) declares a function named function_filename that accepts inputs c,d and returns outputs A.
Whereas A=function_filename(c,d) calls the function named function_filename that accepts inputs c,d and the value returned from the function is stored in A.
For more information please have a look at the following link: https://www.mathworks.com/help/matlab/ref/function.html
