# Array Menu - HP -28S Quick Reference

General
Arrays (or fields) are either vectors or matrices.
Arrays can be real or complex.
If an array contains a single complex value the entire array is
automatically complex.
Lengthy array operations can be interrupted by pressing ON
Arrays are entered by using square brackets [ and ].
Example 2x2 matrix: [[1 2] [3 4]]
+ −
Add/substract vectors or matrices of matching dimensions.
This also works on mixed real/complex arguments but if a complex
argument is involved the result will always be complex.
*
Multiplication. Either operand may be real or complex:
Multiply vector by number or number by vector → vector
Multiply matrix by number or number by matrix → matrix
Multiply matrix by vector → vector
Multiply matrix by matrix → matrix
÷
Calculate matrix X so that M1*X=M2 where M1 and M2 are matrices in
stack level 1 and 2. Or: B A ÷ calculates X=B/A so that AX=B.
Calculate vector X so that M1*X=V2 where M1 and V2 are the matrix
and vector in level 1 and 2. Or: V M ÷ calculates X=V/M so the M*X=V.
These operations produce more accurate results then using the INV
command on matrices. The matrices must be square. Can often be used
even if the matrix A or M is singular and thus solves systems where the
number of variables does not match the number of equations.
INV (1/x)
Returns inverse of square matrix.
SQ (x²)
Returns the square of a square matrix.
→ARRY
Convert stack values into a matrix or vector:
X1 X2 ... Xn n →ARRY results in vector [X1 X2 ... Xn]
X11 X12 ... Xnm {n m} →ARRY results in matrix [[X11...X1m] ...
[Xn1...Xnm]]
Note that combining a number of vectors into a matrix is not possible!
An error occurs if the stack doesn't hold enough values for the matrix or
if they are not of numerical type.
If any one value on the stack is complex the resulting array will be
complex.
The inverse operation of →ARRY. Vector and matrix dimensions are
ARRY→
returned as a number or length-2 list in stack level 1.
PUT
Replace value of a matrix or vector:
V {idx} X PUT puts the number X into vector V at position idx and
returns the modified vector in level 1.
M {row col} X PUT puts the number X into matrix M at position
(row,col) and returns the modified matrix in level 1.
'Nam' {idx} X PUT puts the number X into vector named Nam at
position idx and returns nothing.
When P2 is invoked it calls P1 with the values in stack level 1 and 2
and adds the results that P1 produced (which is ln(x²)+1).

HP-28S
8  