code: def exp_decay(initial, final, begin, duration, t):
      assert final > 0
      assert duration > 0
      # half_life = math.log(2) / math.log(initial / final) * duration
      decay_rate = math.log(initial / final) / duration
      x = initial * math.exp(-decay_rate * (t - begin))
      return max(min(x, initial), final)
  
imports: import argparse
  import math
  import os
  import time
  from functools import partial
  import numpy
  import torch
  import visdom
  from air import AIR, latents_to_tensor
  from viz import draw_many, tensor_to_objs
  import pyro
  import pyro.contrib.examples.multi_mnist
  import pyro.optim
  import pyro.poutine
  from pyro.contrib.examples.util import get_data_directory
  from pyro.infer import SVI, JitTraceGraph_ELBO, TraceGraph_ELBO
label_desc: Use image node_id 4 for calling a global function with example usage: exp_decay(initial, final, begin, duration, t) and returns: max