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
If you find incomplete entry distracting, you may wish to enter vectors and complex numbers as algebraic formulas by pressing the apostrophe key.