An adjacency matrix is a matrix representation of a graph...How do you intend to find an adjacency matrix of matrix?

Well, the easy way is

adjugate(a) = det(a)a^-1

but this only works if a is invertible. If not, I guess you could just manually compute each cofactor:

Define adjugate(a)=
Func
   Local adj,c,i,j,k,n
   n:=rowDim(a)
   adj:=newMat(n,n)
   For i,1,n
      For j,1,n
         c:=a
         For k,1,n
            c[j,k]:=0
            c[k,i]:=0
         EndFor
         c[j,i]:=1
         adj[i,j]:=det(c)
      EndFor
   EndFor
   Return adj
EndFunc