Section 12: Calculating with Matrices 147

Example: Recall the element in row 2, column 1 of matrix A from the previous example. Use the stack registers.

Keystrokes

Display

 

2 v1

1

Enters row number into Y-

 

 

register and column number into

 

 

X-register.

lA

4.0000

Value of a21.

Storing a Number in All Elements of a Matrix

To store a number in all elements of a matrix, simply key that number into the display, then press O> followed by the letter key specifying the matrix.

Matrix Operations

In many ways, matrix operations are like numeric calculations. Numeric calculations require you to specify the numbers to be used; often you define a register for storing the result. Similarly, matrix calculations require you to specify one or two matrices that you want to use. A matrix descriptor is used to specify a particular matrix. For many calculations, you also must specify a matrix for storing the result. This is the result matrix.

Because matrix operations usually require many individual calculations, the calculator flashes the running display during most matrix operations.

Matrix Descriptors

Earlier in this section you saw that when you press l>followed by a letter key specifying a matrix, the name of the matrix appears at the left of the display and the number of rows followed by the number of columns appears at the right. The matrix name is called the descriptor of the matrix. Matrix descriptors can be moved among the stack and data storage registers just like a number – that is, using O, l, v, etc. Whenever a matrix descriptor is displayed in the X-register, the current dimensions of that matrix are shown with it.

You use matrix descriptors to indicate which matrices are used in each matrix operation. The matrix operations discussed in the rest of this section