For my question at https://economics.stackexchange.com/questions/42481/understanding-vernon-smiths-1962-an-experimental-study-of-competitive-market-b

vernon_smith.py

#!/usr/bin/env python3

import numpy as np
import matplotlib.pyplot as plt

buyers = [3.25 - 0.25*n for n in range(0, 11)]
sellers = [3.25 - 0.25*n for n in range(0, 11)]
price_deltas = [0.01 * x for x in range(0, 1000)]

trading_prices = []
trading_counts = []

for _ in range(5):
    buyers_still_in_market = list(range(len(buyers)))
    sellers_still_in_market = list(range(len(sellers)))

    transactions = []

    for _ in range(1000):
        # First, a random buyer offers to buy at some price below their number on
        # their card
        b = np.random.choice(buyers_still_in_market)
        delta = np.random.choice(price_deltas)
        buyer_price = max(0, buyers[b] - delta)
        s = np.random.choice(sellers_still_in_market)
        if buyer_price >= sellers[s]:
            transactions.append((b, buyers[b], s, sellers[s], buyer_price))
            buyers_still_in_market.remove(b)
            sellers_still_in_market.remove(s)
            trading_prices.append(buyer_price)

        # Then, a random seller offers to sell at some price above their number on
        # their card.
        s = np.random.choice(sellers_still_in_market)
        delta = np.random.choice(price_deltas)
        seller_price = sellers[s] + delta
        b = np.random.choice(buyers_still_in_market)
        if seller_price <= buyers[b]:
            transactions.append((b, buyers[b], s, sellers[s], seller_price))
            buyers_still_in_market.remove(b)
            sellers_still_in_market.remove(s)
            trading_prices.append(seller_price)

    trading_counts.append(len(trading_prices))

    print(len(transactions), "transactions")

plt.plot(list(range(len(trading_prices))), trading_prices)
plt.ylim(0, 4.00)
for x in trading_counts:
    plt.axvline(x=x-1, ymin=0, ymax=4.0, color='red')
    print("line drawn at x =", x)
plt.show()