Function to add two matrices mod 2

Question

I have:

lightstep[m_, gg_] :=
 Which[gg == {1, 1}, m = Mod[m + m, 2]]

Then I entered:

A = {{1, 1, 0}, {1, 0, 0}, {0, 0, 0}}

And I tried:

lightstep[A, {1, 1}]

And got this message:

Set::setraw: Cannot assign to raw object 1.

Set::setraw: Cannot assign to raw object 0.

General::stop: Further output of Set::setraw will be suppressed during this calculation.

And this output:

{{0, 0, 0}, {0, 0, 0}, {0, 0, 0}}

Why the message?

Update: Thanks for the help everyone. I was able to complete my project.

lightstep[m_, gg_] := Module[{
   m1 = {{1, 1, 0}, {1, 0, 0}, {0, 0, 0}},
   m2 = {{1, 1, 1}, {0, 1, 0}, {0, 0, 0}},
   m3 = {{0, 1, 1}, {0, 0, 1}, {0, 0, 0}},
   m4 = {{1, 0, 0}, {1, 1, 0}, {1, 0, 0}},
   m5 = {{0, 1, 0}, {1, 1, 1}, {0, 1, 0}},
   m6 = {{0, 0, 1}, {0, 1, 1}, {0, 0, 1}},
   m7 = {{0, 0, 0}, {1, 0, 0}, {1, 1, 0}},
   m8 = {{0, 0, 0}, {0, 1, 0}, {1, 1, 1}},
   m9 = {{0, 0, 0}, {0, 0, 1}, {0, 1, 1}}
   },
  Which[
   gg == {1, 1}, Mod[m + m1, 2],
   gg == {1, 2}, Mod[m + m2, 2],
   gg == {1, 3}, Mod[m + m3, 2],
   gg == {2, 1}, Mod[m + m4, 2],
   gg == {2, 2}, Mod[m + m5, 2],
   gg == {2, 3}, Mod[m + m6, 2],
   gg == {3, 1}, Mod[m + m7, 2],
   gg == {3, 2}, Mod[m + m8, 2],
   gg == {3, 3}, Mod[m + m9, 2]
   ]]

Then:

DynamicModule[
 {m = {{1, 1, 0}, {1, 0, 0}, {0, 0, 0}}, gg = {0, 0}},
 Dynamic@(
   If[gg == {0, 0}, {}, m = lightstep[m, gg]; gg = {0, 0}]; 
   Pane[TableForm[
     MapIndexed[
      Button["   ", gg = #2, ImageSize -> {420/(3 + 1), 420/(3 + 1)}, 
        Background -> {Black, RGBColor[1, .81, 0]}[[1 + #1]]] &, 
      m, {2}]], {450, 450}, Alignment -> Center]
   )]

This was with help from (http://demonstrations.wolfram.com/LightsOutPuzzle/)[http://demonstrations.wolfram.com/LightsOutPuzzle/]

You need HoldFirst or friends. Take a look here: Attempting to make an assignment to the argument of a function — Kuba, Nov 19 '16 at 20:49
lightstep[m_, gg_] := Which[gg == {1, 1}, Return[Mod[m + m, 2]]] will add two matrices mod 2. If you want to modify your original matrix, you could then use A = lightstep[A, {1, 1}] — Chris K, Nov 19 '16 at 21:34
When m is a matrix over the Galois field {0, 1} , Mod[m + m, 2] is mathematically the zero matrix with same dimensions as m. If the 1st argument of lightship is such a matrix, it is better written lightstep[m_, gg_] := Which[gg == {1, 1}, ConstantArray[0, Dimensions[m]]] — m_goldberg, Nov 19 '16 at 22:10
You can not assign to a formal argument of a function within the function body. Formal arguments appearing the body are replaced by their passed value before any assignments done in the body are evaluated. — m_goldberg, Nov 19 '16 at 22:11

Function to add two matrices mod 2

0 Answers0