docs: def symbol_list(what_list):
      '''
      provide default symbol lists
  
      Parameters
      ----------
      what_list : string
          String name of symbol lists provided; "list1", "list2",
          "lines1" or "lines2".
  
      '''
      if what_list is "list1":
          symbol=['ro','bo','ko','go','mo'\
                  ,'r-','b-','k-','g-','m-','r--','b--','k--'\
                  ,'g--','r1']
          #symbol=['r+','ro','r-']
      elif what_list is "list2":
          symbol=['r-','b--','g-.','k:','md','.','o','v','^','<','>','1','2',\
                  '3','4','s','p','*','h','H','+']
      elif what_list is "lines1":
          symbol=['b--','k--','r--','c--','m--','g--','b-','k-','r-','c-','m-','g-','b.','b-.','k-.','r-.','c-.','m-.','g-.','b:','k:','r:','c:','m:','g:']
      elif what_list is "lines2":
          symbol=['g:','r-.','k-','b--','k-.','b+','r:','b-','c--','m--','g--','r-','c-','m-','g-','k-.','c-.','m-.','g-.','k:','r:','c:','m:','b-.','b:']
      return symbol