docs: def heatmap(n_x=5,n_y=10):
  	"""
  	Returns a DataFrame with the required format for 
  	a heatmap plot
  
  	Parameters:
  	-----------
  		n_x : int
  			Number of x categories
  		n_y : int
  			Number of y categories
  	"""	
  	x=['x_'+str(_) for _ in range(n_x)]
  	y=['y_'+str(_) for _ in range(n_y)]
  	return pd.DataFrame(surface(n_x-1,n_y-1).values,index=x,columns=y)