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10 Matrices
Despite of its small display one of the nice features of HP-42S is the ability to work with matrices.
This is done using basically the ▀ MATRIX menu.
This multi-line menu has the following items:
NEW, INV, DET, TRAN, SIMQ, EDIT
DOT, CROSS, UVEC, DIM, INDEX, EDITN
STOIJ, RCLIJ, STOEL, RCLEL, PUTM, GETM
Let's start from the first line.
NEW: This function creates a new matrix of a given size. Line y of the stack should contain the
number of rows and line x should contain the number of columns. For example:
3 ENTER 2 ▀ MATRIX NEW creates a 3x2 matrix.
This matrix is empty or null because all elements are zero. (See EDIT)
INV: Calculates the inverse of a matrix in line x of the stack. The given matrix must have the same
number of rows and columns and a non zero determinant.
DET: Calculates the determinant of a matrix in line x of the stack. The given matrix must have the
same number of rows and columns.
TRAN: Calculates the transposition of a matrix. The transpost is another matrix with rows changed
by columns. If A is a matrix nxm and aij is an element of it then its transpost will be a
matrix B where an element bij=aji.
SIMQ: Means “Simultaneous Equations”. We are not going to see this here.
EDIT: This edits a matrix in line x of the stack.
It has the following sub items:
In the first line we have
← OLD ↑ ↓ GOTO → and there is also a second line we are not going to see.
When you call EDIT with a matrix in first line of the stack you are going to see something
like
1:1=0.0000
This means the element (1,1) “line one and column one” of the given matrix is 0.0000.
(Here we are using FIX 4 for the examples)
If you want to change this element just enter the new value.
For example: 5 6 ENTER gives to us 1:1=56.0000.
To change another element it is just go to its position (we use ← or → to change the column
and ↑ or ↓ to change the line we are editing).
One can also use GOTO to go to a specific row and OLD to undo an entered element.
In fact you don't need to press ENTER, just press → to move to the next element.