python - 使用 Python 进行捕食者-猎物模拟。 Python 读取等式错误的问题？

Question

我正在做一个捕食者猎物模拟，打印特定时期内猎物和捕食者的数量。

这是我第一次发帖，如果有任何问题，请告诉我。

我正在实现的测试信息是:

a= .1
b= .01
c= .01
d= .00002
prey_population = 1000
predator_population = 20
periods = 10

a = float(input("Enter the rate at which prey birth exceeds natural death: "))
b = float(input("Enter the rate of predation: "))
c = float(input("Enter the rate at which predator deaths exceed births without food: "))
d = float(input("Predator increase with the presence of food: "))

prey_population = int(input("Enter prey population: "))
predator_population = int(input("Enter predator population: "))

periods = int(input("Enter the number of periods: "))

for i in range(1, periods + 1):
    prey_population = int(prey_population * (1 + a - b * predator_population))
    predator_population = int(predator_population * (1 - c + d * prey_population))

    print("After period", i, "there are", predator_population, "predators")
    print("After period", i, "there are", prey_population, "prey")

我的猎物信息在第 6 个周期之前都是准确的，我的捕食者输出仅在第 3 个周期是准确的。

我的输出是:

After period 1 there are 20 predators
After period 1 there are 900 prey

After period 2 there are 20 predators
After period 2 there are 810 prey

After period 3 there are 20 predators
After period 3 there are 729 prey

After period 4 there are 20 predators
After period 4 there are 656 prey

After period 5 there are 20 predators
After period 5 there are 590 prey

After period 6 there are 20 predators
After period 6 there are 531 prey

After period 7 there are 19 predators
After period 7 there are 477 prey

After period 8 there are 18 predators
After period 8 there are 434 prey

After period 9 there are 17 predators
After period 9 there are 399 prey

After period 10 there are 16 predators
After period 10 there are 371 prey

它应该显示的数字是:

After period 1 there are 20 predators
After period 1 there are 900 prey

After period 2 there are 20 predators
After period 2 there are 808 prey

After period 3 there are 20 predators
After period 3 there are 724 prey

After period 4 there are 21 predators
After period 4 there are 648 prey

After period 5 there are 21 predators
After period 5 there are 580 prey

After period 6 there are 21 predators
After period 6 there are 518 prey

After period 7 there are 21 predators
After period 7 there are 463 prey

After period 8 there are 21 predators
After period 8 there are 413 prey

After period 9 there are 21 predators
After period 9 there are 369 prey

After period 10 there are 21 predators
After period 10 there are 330 prey

Answer 1

在使用新值计算predator_population 之前，每个回合您都会更新prey_population 的值。这会影响结果。