43 lines
1.1 KiB
Python
43 lines
1.1 KiB
Python
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"""
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Sheet 2: Commercial Bank Model.
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Part II — 2.2. Loan creation: dLoans = dDeposits.
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Capital constraint: CR = Equity / RWA >= k. Loans_max = Equity / k.
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"""
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from dataclasses import dataclass
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from typing import Optional
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from fqbm.state import FQBMState
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@dataclass
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class CommercialBankParams:
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"""Parameters for commercial bank credit."""
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k: float = 0.08 # minimum capital ratio (e.g. 8%)
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d_deposits: float = 0.0 # exogenous deposit change → dLoans = dDeposits
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def commercial_bank_step(
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state: FQBMState,
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params: Optional[CommercialBankParams] = None,
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) -> FQBMState:
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"""
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Apply one period: dLoans = dDeposits (endogenous money). Equity unchanged unless losses.
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"""
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params = params or CommercialBankParams()
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out = state.copy()
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out.Loans += params.d_deposits
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out.Deposits += params.d_deposits
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return out
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def loans_max(equity: float, k: float) -> float:
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"""Maximum credit capacity: Loans_max = Equity / k (Part II — 2.2)."""
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return equity / k if k > 0 else 0.0
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def capital_ratio(equity: float, rwa: float) -> float:
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"""CR = Equity / RWA."""
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return equity / rwa if rwa > 0 else 0.0
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