Adjoint matrix (my function): ok with numbers but not symbolics

[salvomic]

Here there is the code, if someone would like to collaborate to find the error in it, that prevent the use of a letters instead of numbers in the matrix:

Code:


minor();

EXPORT cofactors(m)
// Cofactors of the matrix m
BEGIN
local tempmat, cofact, deter;
local r, c, j, k;
  r:=rowDim(m);
  c:=colDim(m);
  cofact:=  MAKEMAT(0,r,c);
  tempmat:= m;
  FOR j FROM 1 TO r DO
  FOR k FROM 1 to c DO
    cofact:= minor(m, j, k);
    deter:= ((-1)^(j+k)) * det(cofact);
    tempmat(j,k):= deter;
  END; // inner for
  END; //for
  RETURN tempmat;
END;

minor(mat, r,c)
// Returns the matrix without row r and col c
BEGIN
  mat:= delrows(mat,r);
  mat:= delcols(mat,c);
  RETURN mat;
END;

EXPORT adj(m)
// adjoint matrix (=transpose of cofactors(m))
BEGIN
local ad;
  ad:= cofactors(m);
RETURN TRN(ad);
END;

The problem is in input, I suppose:
type([1,2],[4,3]) -> DOM_LIST
TYPE([1,2],[4,3]) -> 4
(matrix)
but
type([1,sin(x)],[2,3]) -> DOM_LIST
TYPE([1,sin(x)],[2,3]) -> 6
(list)
...