154 Section 12: Calculating with Matrices

Keystrokes

Display

 

 

-

C

 

2

3

Calculates B - A and stores

 

 

 

 

 

values in redimensioned result

 

 

 

 

 

matrix C.

The result is

⎡0

1

2⎤

 

 

C =

 

 

 

 

3

4

8

 

 

Matrix Multiplication

With matrix description in both the X- and Y-registers, you can calculate three different matrix products. The table below shows the results of the three functions for a matrix X specified in the X-register and a matrix Y specified in the Y-register. The matrix X-1is the inverse of X, and the matrix YT is the transpose of Y.

Pressing

Calculates*

*

YX

´>5

YTX

÷

X-1Y

*Result is stored in result matrix. For ÷, the result matrix can be Y but not X. For the others, the result matrix must be other than X or Y.

Note: When you use the ÷ function to evaluate the expression A-1B, you must enter the matrix descriptors in the order B, A rather than in the order that they appear in the expression.*

The value stored in each element of the result matrix is determined according to the usual rules of matrix multiplication.

For > 5, the matrix specified in the Y-register isn't changed by this operation, even though its transpose is used. The result is identical to that obtained using >4 (transpose) and *.

*This is the same order you would use if you were entering b and a for evaluating a-1b = b/a

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Image 154
HP 15c Scientific manual Matrix Multiplication