Cross in Matrix
10-15-2014, 06:52 PM
Post: #1
 nakjaen Junior Member Posts: 13 Joined: Sep 2014
Cross in Matrix
How i can input a matrix and have a cross product?

ex.
i j k
2 3 1
1 2 3

and i need a det.
solution: 1i + 2j +3k

my hp prime say error when i input Cross( M1 )
M1= i j k
2 3 1
1 2 3

in hp50g is easy but here
10-15-2014, 08:48 PM (This post was last modified: 10-15-2014 08:51 PM by Han.)
Post: #2
 Han Senior Member Posts: 1,882 Joined: Dec 2013
RE: Cross in Matrix
cross() takes two vectors and computes the cross product; one way to do this is to compute the determinant of the matrix you described. So if you already have the matrix, you want to use the det() command

So either use:

cross([2,3,1],[1,2,3]) to get [7 -5 1] or use
$\mathrm{det}\left( \left[ \begin{array}{rrr} i & j & k \\ 2 & 3 & 1\\ 1 & 2 & 3 \end{array} \right] \right)$
to get $$7\vec{i} - 5\vec{j}+\vec{k}$$

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10-16-2014, 01:48 AM
Post: #3
 mlpalacios8 Junior Member Posts: 6 Joined: Sep 2014
RE: Cross in Matrix
Handling matrixes is more efficient in the Prime than in the 50g.

I recommend you to use CAS and the matrix templates.

Put the command and then manually enter the matrix using the matrix template (1st row, last column).
The comma button serves as a "next column".

This is very helpful to solve linear system of equations too (inverse coefficient matrix * contant matrix, RREF command, etc).

After a couple of minutes, you will see how efficient the Prime is with matrixes thanks to the big touchscreen.
06-23-2015, 01:59 AM
Post: #4
 rgallier Junior Member Posts: 27 Joined: Feb 2015
RE: Cross in Matrix
Why does
det( [ [ i j k ] , [ 2 3 1 ] , [ 1 2 3 ] ])
return
-6.48*j+2.04*k-0.24*i
-0.24*i-6.48*j+2.04*k
06-23-2015, 12:27 PM
Post: #5
 Joe Horn Senior Member Posts: 2,004 Joined: Dec 2013
RE: Cross in Matrix
(06-23-2015 01:59 AM)rgallier Wrote:  Why does
det( [ [ i j k ] , [ 2 3 1 ] , [ 1 2 3 ] ])
return
-6.48*j+2.04*k-0.24*i
-0.24*i-6.48*j+2.04*k

"i" is always put at the end because "i" is not a variable, but is the constant i. Try h+i+j; it returns h+j+i. Never use i or e as variables, because they aren't.

<0|ΙΈ|0>
-Joe-
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