I discovered it during Machine learnin courses on Coursera
To specify the actual function we are minimizing, we use a "short-hand" for specifying functions with the @(t) ( costFunction(t, X, y) ) . This creates a function, with argument t, which calls your costFunction. This allows us to wrap the costFunction for use with fminunc.
@(t) ( costFunction(t, X, y) ) - that’s awesome