An empty vector or in another words, a vector which stores no values, can be generated using the empty square brackets:
>> evec = 
evec = 
ans = 0
Then, values can be added to the vector by concatenating, or by adding values to the existing vector. The statement below takes what is presently in evec that is nothing, and adds a 4 to it.
>> evec = [evec 4]
evec = 4
The statement below takes what is presently in evec that is 4, and adds an 11 to it.
>> evec = [evec 11]
evec = 4 11
This can be continued as numerous times as desired, in order to build a vector up from nothing.