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Mod Isn't Working

Posted 11 years ago
My assignment is to decode the message FVRMTGJTJJRMULSIRGBEMRNVFRC which was encoded
using the key matrix B. This is what I did. Can someone please tell me what I am doing wrong. Thank you.
 B = {{4, 9, 15}, {15, 17, 6}, {24, 0, 17}}
 R is the message put into numbers where A is 0, B is 1 and so on to Z being 25
 R = {{5, 12, 9, 9, 20, 8, 1, 17, 5}, {21, 19, 19, 17, 11, 17, 4, 13,
    17}, {17, 6, 9, 12, 18, 6, 12, 21, 2}}
 
 b = Inverse[b]
 {{-(289/5963), 153/5963, 3/89}, {111/5963, 292/5963, -(3/89)}, {408/
   5963, -(216/5963), 1/89}}
 
J = Dot[b, R]
{{5185/5963, 645/5963, 2115/5963, 36/89, -(479/5963), 1495/5963, 2735/
  5963, 1297/5963, 1558/5963}, {3270/5963, 5674/5963, 4738/5963, 53/
  89, 1814/5963, 4646/5963, -(1133/5963), 1462/5963, 5117/
  5963}, {-(1357/5963), 1194/5963, 171/5963, 12/89, 6990/
  5963, -(6/5963), 348/5963, 5535/5963, -(1498/5963)}}

L = Mod[J, 26]
{{5185/5963, 645/5963, 2115/5963, 36/89, 154559/5963, 1495/5963, 2735/
  5963, 1297/5963, 1558/5963}, {3270/5963, 5674/5963, 4738/5963, 53/
  89, 1814/5963, 4646/5963, 153905/5963, 1462/5963, 5117/
  5963}, {153681/5963, 1194/5963, 171/5963, 12/89, 6990/5963, 155032/
  5963, 348/5963, 5535/5963, 153540/5963}}
POSTED BY: Kyle Lammers
3 Replies
What is the line
b = Inverse
supposed to produce?
POSTED BY: Daniel Lichtblau
Posted 11 years ago
b = Inverse takes the inverse of B
the output I get is:
{{-(289/5963), 153/5963, 3/89}, {111/5963, 292/5963, -(3/89)}, {408/
  5963, -(216/5963), 1/89}}
POSTED BY: Kyle Lammers
Maybe you want
b = Inverse[B, Modulus -> 26]
(And don't forget to transpose, eventually.)
POSTED BY: Daniel Lichtblau
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