docs: def getGenoIndex(self,pos0=None,pos1=None,chrom=None,pos_cum0=None,pos_cum1=None):
          """computes 0-based genotype index from position of cumulative position. 
          Positions can be given in one out of two ways: 
          - position (pos0-pos1 on chrom)
          - cumulative position (pos_cum0-pos_cum1)
          If all these are None (default), then all genotypes are returned
  
          Args:
              pos0:       position based selection (start position)
              pos1:       position based selection (stop position)
              chrom:      position based selection (chromosome)
              pos_cum0:   cumulative position based selection (start position)
              pos_cum1:   cumulative position based selection (stop position)
          
          Returns:
              i0:         genotype index based selection (start index)
              i1:         genotype index based selection (stop index)
          """
          if (pos0 is not None) & (pos1 is not None) & (chrom is not None):
              I = self.gneoChrom==chrom
              I = I & (self.genoPos>=p0) & (self.genoPos<p1)
              I = SP.nonzero(I)[0]
              i0 = I.min()
              i1 = I.max()
          elif (pos_cum0 is not None) & (pos_cum1 is not None):
              I = (self.genoPos_cum>=pos_cum0) & (self.genoPos_cum<pos_cum1)
              I = SP.nonzero(I)[0]
              if I.size==0:
                  return None
              i0 = I.min()
              i1 = I.max()
          else:
              i0=None
              i1=None
          return i0,i1