setdiag <- function(M, v) {
  stop("needs translation")
  # function M = setdiag(M, v)
  # % SETDIAG Set the diagonal of a matrix to a specified scalar/vector.
  # % M = set_diag(M, v)

  # n = length(M);
  # if length(v)==1
  #   v = repmat(v, 1, n);
  # end

  # % e.g., for 3x3 matrix,  elements are numbered
  # % 1 4 7
  # % 2 5 8
  # % 3 6 9
  # % so diagnoal = [1 5 9]


  # J = 1:n+1:n^2;
  # M(J) = v;
}