# Homework Help: Matrix code

1. Aug 21, 2009

### gtfitzpatrick

1. The problem statement, all variables and given/known data

in coding a msg, a black space was represented by 0, an A by 1,a B by 2 etc...The msg was transformed using the matrix

-1 -1 2 0
1 1 -1 0
0 0 -1 1
1 0 0 -1

and sent out as -19,19,25,-21,0,18,-18,15,3,10,-8,3,-2,20,-7,12

so what i've tried is...

so to reverse the transform i think i get the inverse of the transform matrix and multiply by the outputed answer

for the inverse i got

1 1 1 1
0 1 -1 -1
1 1 0 0
1 1 1 0

and multiplied it by
-19 19 25 -21
0 18 -18 15
3 10 -8 3
-2 20 -7 12

and got

-18 67 -8 9
-1 -12 -3 0
-19 37 7 -6
-16 47 -1 -3

which i was just going to convert back into letters to get the msg,but what letter is 67 or 37...

Confussed...

Last edited: Aug 21, 2009
2. Aug 21, 2009

### Dick

You aren't supposed to multiply the inverse by the matrix of all of the integers in the message, you are supposed to multiply it by each of the column vectors [-19,19,25,-21]^T, [0,18,-18,15]^T etc. You could also transpose your data matrix.

3. Aug 21, 2009

### gtfitzpatrick

thats dick, i'd just figured it out, i was just putting the coded msg in the wrong way round---the msg reads - do your homework-very good