Brackets at the start of input in matlab ?? [ x , y ] =

I would like to know what is the use of having inputs in brackets like this :

[fx, fx开发者_StackOverflow中文版x] = differentiate(...) why is fx and fxx in square brackets ?

Another example includes this [y,t,ysd] = step(m)

Please explain !

Thanks

Matlab allows multiple return values. fx and fxx will each be assigned a return value of the function.