code: def apply_K(df, k):
      
      if 'k' not in df.columns:
          df['k'] = k
  
      if 'rho_a' not in df.columns:
          df['rho_a'] = df['r'] * df['k']
  
      if 'sigma_a' not in df.columns:
          df['sigma_a'] = 1.0 / df['rho_a']
  
      if 'Zt' in df.columns:
          df['rho_a_complex'] = df['Zt'] * df['k']
      return df
docs: Apply the geometric factors to the dataset and compute (apparent)
      resistivities/conductivities