question: public ArrayFieldVector ( T [ ] v1 , FieldVector < T > v2 ) throws NullArgumentException { MathUtils . checkNotNull ( v1 ) ; MathUtils . checkNotNull ( v2 ) ; field = v2 . getField ( ) ; final T [ ] v2Data = ( v2 instanceof ArrayFieldVector ) ? ( ( ArrayFieldVector < T > ) v2 ) . data : v2 . toArray ( ) ; data = MathArrays . buildArray ( field , v1 . length + v2Data . length ) ; System . arraycopy ( v1 , 0 , data , 0 , v1 . length ) ; System . arraycopy ( v2Data , 0 , data , v1 . length , v2Data . length ) ; }
target:  Construct a vector by appending one vector to another vector.