code: def surface(n_x=20,n_y=20):
  		
  	x=[float(np.random.randint(0,100))]
  	for i in range(n_x):
  		x.append(x[:1][0]+np.random.randn()*np.random.randint(1,10))
  	df=pd.DataFrame(x)
  	for i in range(n_y):
  		df[i+1]=df[i].map(lambda x:x+np.random.randn()*np.random.randint(1,10))
  	return df
docs: Returns a DataFrame with the required format for 
  	a surface plot
  
  	Parameters:
  	-----------
  		n_x : int
  			Number of points along the X axis
  		n_y : int
  			Number of points along the Y axis