DiagMat(L: LIST): MAT
DiagMat(R: RING, L: LIST): MAT

/**/  DiagMat([3,4,5]);
matrix(
[
  [3, 0, 0],
  [0, 4, 0],
  [0, 0, 5]
])

/**/ DiagMat(QQ,[5,6,7]);
matrix(
[
  [5, 0, 0],
  [0, 6, 0],
  [0, 0, 7]
])

-- fast implementation for high powers of a diagonal matrix
/**/  Define PowerDiag(M, Exp)
/**/    If not(IsDiagonal(M)) Then
/**/      error("PowerDiag: matrix must be diagonal");
/**/    EndIf;
/**/    Return DiagMat([ M[I, I]^Exp | I In 1..NumRows(M) ]);
/**/  EndDefine;

/**/ PowerDiag(IdentityMat(QQ,3), 200000000);
matrix(QQ,
 [[1, 0, 0],
  [0, 1, 0],
  [0, 0, 1]])