docs: def fit(self, index, distvec, recalc=False, dimensions=3):
          """
          Replace distance matrix values at row/column index with
          distances in distvec, and compute new coordinates.
          Optionally use distvec to update means and (potentially) 
          get a better estimate.
          distvec values should be plain distances, not squared
          distances.
          """
          brow = self.new_B_row(index, distvec**2, recalc)
          return self.new_coords(brow)[:dimensions]