code: def gtval0(f, c1, c2):
      r"""For positive values in the first column of the dataframe
      that are greater than the second column, get the value in
      the first column, otherwise return zero.
  
      Parameters
      ----------
      f : pandas.DataFrame
          Dataframe containing the two columns ``c1`` and ``c2``.
      c1 : str
          Name of the first column in the dataframe ``f``.
      c2 : str
          Name of the second column in the dataframe ``f``.
  
      Returns
      -------
      new_val : float
          A positive value or zero.
  
      """
      if f[c1] > f[c2] and f[c1] > 0:
          new_val = f[c1]
      else:
          new_val = 0
      return new_val
  
imports: from alphapy.calendrical import biz_day_month
  from alphapy.calendrical import biz_day_week
  from alphapy.globals import NULLTEXT
  from alphapy.globals import BSEP, PSEP, USEP
  from alphapy.variables import vexec
  import itertools
  import logging
  import math
  import numpy
  import pandas
label_desc: Use image node_id 23 for calling a global function with example usage: gtval0(f, c1, c2) and returns: new_val