docs: def mindx(m, nmax, mmax):
      """index to the first n value for a give m within the spherical 
      coefficients vector. Used by sc_to_fc"""
  
      ind = 0
      NN = nmax + 1
  
      if np.abs(m) > mmax:
          raise Exception("|m| cannot be larger than mmax")
  
      if (m != 0):
          ind = NN
          ii = 1
          for i in xrange(1, np.abs(m)):
              ind = ind + 2 * (NN - i)
              ii = i + 1
  
          if m > 0:
              ind = ind + NN - ii
  
      return ind