diff --git a/A/4/A4_to_csv.py b/A/4/A4_to_csv.py
new file mode 100644
index 0000000..54c2f0c
--- /dev/null
+++ b/A/4/A4_to_csv.py
@@ -0,0 +1,19 @@
+import json
+with open("A4_res.json", "r") as file:
+  content=json.load(file)
+fout1=open("tmp1.dat","w")
+for node_point in range(224):
+  for time_point in range(201):
+    v=content[time_point][node_point]["v"]
+    print(v,'\t',file=fout1,sep="",end="")
+  print('\n',file=fout1,end="",sep="")
+fout2=open("tmp2.dat","w")
+for node_point in range(224):
+  for time_point in range(201):
+    x=content[time_point][node_point]["node"][0]
+    print(x,'\t',file=fout2,sep="",end="")
+  print('\n',file=fout2,end="",sep="")
+  for time_point in range(201):
+    y=content[time_point][node_point]["node"][1]
+    print(y,'\t',file=fout2,sep="",end="")
+  print('\n',file=fout2,end="",sep="")
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diff --git a/A/4/seek_max.py b/A/4/seek_max.py
new file mode 100644
index 0000000..4adcf54
--- /dev/null
+++ b/A/4/seek_max.py
@@ -0,0 +1,35 @@
+from simulator import *
+
+kTiBeg = -100
+kTiEnd = 100
+kSampleNum = 1000
+kStep = (kTiEnd - kTiBeg) / kSampleNum
+kParallelNum=24
+tasks_list = [i for i in np.arange(kTiBeg, kTiEnd, kStep)]
+for i in np.arange(0, 10, 0.1):
+  tasks_list.append(i)
+for i in np.arange(5, 10, 5.0/1000):
+  tasks_list.append(i)
+task_list_per_process=[tasks_list[i::kParallelNum] for i in range(kParallelNum)]
+
+print(f"len(task_list_per_thread)={len(task_list_per_process)}",file=sys.stderr)
+def ProcessEntryPoint(arg):
+  ti_list, process_id = arg
+  orbit = GoodOrbit()
+  loong = Loong(orbit, 224, mp.mpf("1.0"), mp.mpf("1e-8"))
+  max_speed_found=mp.mpf("0.0")
+  for ti in ti_list:
+    print(f"calculating time_point={ti}",file=sys.stderr)
+    res = loong.CalcStatusListByTime(mp.mpf(ti))
+    for node in res:
+      max_speed_found=max(max_speed_found,node["v"])
+  return max_speed_found
+
+if __name__ == "__main__":
+  manager = multiprocessing.Manager()
+  task_args_list = [(task_list_per_process[i], i) for i in range(kParallelNum)]
+  with multiprocessing.Pool(processes=kParallelNum) as pool:
+    res_list=pool.map(ProcessEntryPoint, task_args_list)
+  max_speed_found=max(res_list)
+  valid_head_speed = mp.mpf("1.0") * (mp.mpf("2.0")/max_speed_found)
+  print(f"max_speed_found={max_speed_found}, valid_head_speed={valid_head_speed}")
\ No newline at end of file