When ( or [ is typed to begin entering a complex number or vector, respectively, the effect is to push an incomplete complex number or vector onto the stack. The , key adds the value(s) at the top of the stack onto the current incomplete object. The ) and ] keys "close" the incomplete object after adding any values on the top of the stack in front of the incomplete object.
As a result, the sequence of keystrokes [ 2 , 3 RET 2 * , 9 ] pushes the vector `[2, 6, 9]' onto the stack. Likewise, ( 1 , 2 Q ) pushes the complex number `(1, 1.414)' (approximately).
If several values lie on the stack in front of the incomplete object, all are collected and appended to the object. Thus the , key is redundant: [ 2 RET 3 RET 2 * 9 ]. Some people prefer the equivalent SPC key to RET.
As a special case, typing , immediately after (, [, or , adds a zero or duplicates the preceding value in the list being formed. Typing DEL during incomplete entry removes the last item from the list.
The ; key is used in the same way as , to create polar complex numbers: ( 1 ; 2 ). When entering a vector, ; is useful for creating a matrix. In particular, [ [ 1 , 2 ; 3 , 4 ; 5 , 6 ] ] is equivalent to [ [ 1 , 2 ] , [ 3 , 4 ] , [ 5 , 6 ] ].
Incomplete entry is also used to enter intervals. For example,
[ 2 .. 4 ) enters a semi-open interval. Note that when you type
the first period, it will be interpreted as a decimal point, but when
you type a second period immediately afterward, it is re-interpreted as
part of the interval symbol. Typing .. corresponds to executing
the calc-dots command.
If you find incomplete entry distracting, you may wish to enter vectors and complex numbers as algebraic formulas by pressing the apostrophe key.