FA-58646 / Loan amortization schedules / Open access

Payoff quote with per diem: per diem rounding stage · case 01

Payoff interest does not equal the quoted per diem times the days.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Interest is rounded once over all days instead of multiplying the rounded per diem.

THE FAILURE

Interest is rounded once over all days instead of multiplying the rounded per diem.

Unsuccessful approach: Truncating the per diem keeps the multiplication but understates the daily charge.

Case contract

x = {'balance', 'rate_bp', 'last_paid_day', 'payoff_day', 'basis', 'fees_due', 'escrow' (credit, may be negative), 'penalty_bp', 'penalty_until'}. Per diem = round_half_up(balance*bp/(10000*basis)); interest = per diem * (payoff_day - last_paid_day). Penalty = round_half_up(balance*penalty_bp/10000) when payoff_day <= penalty_until, else 0. Payoff = balance + interest + fees + penalty - escrow. Return {'per_diem', 'interest', 'penalty', 'payoff'}.

Why this case matters

Amortization engines drive borrower statements, payoff quotes and investor remittances; a misplaced rounding step, boundary or ordering rule compounds across hundreds of periods.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    def rnd(n, d):
        q, r = divmod(n, d)
        return q + (1 if 2 * r >= d else 0)
    per_diem = rnd(x['balance'] * x['rate_bp'], 10000 * x['basis'])
    days = x['payoff_day'] - x['last_paid_day']
    interest = rnd(x['balance'] * x['rate_bp'] * days, 10000 * x['basis'])
    penalty = rnd(x['balance'] * x['penalty_bp'], 10000) if x['payoff_day'] <= x['penalty_until'] else 0
    payoff = x['balance'] + interest + x['fees_due'] + penalty - x['escrow']
    return {'per_diem': per_diem, 'interest': interest, 'penalty': penalty, 'payoff': payoff}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: per diem rounding stage', {'balance': 100000, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 145, 'basis': 360, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 115}, {'per_diem': 17, 'interest': 765, 'penalty': 0, 'payoff': 108265}], ['control 1', {'balance': 999999, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 10}, {'per_diem': 164, 'interest': 164, 'penalty': 0, 'payoff': 1000163}], ['control 2', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 160}, {'per_diem': 2029, 'interest': 2029, 'penalty': 246914, 'payoff': 12598121}], ['control 3', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 360, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 70}, {'per_diem': 347, 'interest': 347, 'penalty': 20000, 'payoff': 1011846}], ['control 4', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 130}, {'per_diem': 2058, 'interest': 2058, 'penalty': 246914, 'payoff': 12582650}], ['control 5', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 0, 'penalty_until': 115}, {'per_diem': 12, 'interest': 12, 'penalty': 0, 'payoff': 103512}], ['control 6', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 115}, {'per_diem': 2058, 'interest': 2058, 'penalty': 246914, 'payoff': 12598150}]], [['regression: per diem rounding stage', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 46, 'basis': 365, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 100, 'penalty_until': 1}, {'per_diem': 342, 'interest': 15390, 'penalty': 0, 'payoff': 1022889}], ['regression: per diem rounding stage, partial-repair probe', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 61}, {'per_diem': 13, 'interest': 13, 'penalty': 2000, 'payoff': 105513}], ['control 1', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 31, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 0, 'penalty_until': 61}, {'per_diem': 125, 'interest': 3750, 'penalty': 0, 'payoff': 1007249}], ['control 2', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 40}, {'per_diem': 4228, 'interest': 4228, 'penalty': 0, 'payoff': 12337906}], ['control 3', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 130}, {'per_diem': 12, 'interest': 12, 'penalty': 2000, 'payoff': 90012}], ['control 4', {'balance': 12345678, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 200, 'penalty_until': 40}, {'per_diem': 1522, 'interest': 1522, 'penalty': 246914, 'payoff': 12598114}], ['control 5', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 100}, {'per_diem': 342, 'interest': 342, 'penalty': 0, 'payoff': 1000341}]], [['regression: per diem rounding stage', {'balance': 5000, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 55, 'basis': 365, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 40}, {'per_diem': 1, 'interest': 45, 'penalty': 0, 'payoff': 9045}], ['control 1', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 100, 'penalty_until': 1}, {'per_diem': 34, 'interest': 34, 'penalty': 0, 'payoff': 91534}], ['control 2', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 100}, {'per_diem': 4287, 'interest': 4287, 'penalty': 0, 'payoff': 12337965}], ['control 3', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 40, 'basis': 360, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 100, 'penalty_until': 10}, {'per_diem': 125, 'interest': 3750, 'penalty': 0, 'payoff': 995249}], ['control 4', {'balance': 100000, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 360, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 100, 'penalty_until': 10}, {'per_diem': 17, 'interest': 17, 'penalty': 0, 'payoff': 104017}], ['control 5', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 160}, {'per_diem': 2058, 'interest': 2058, 'penalty': 0, 'payoff': 12355236}], ['control 6', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 100}, {'per_diem': 4287, 'interest': 4287, 'penalty': 0, 'payoff': 12349965}]], [['regression: per diem rounding stage', {'balance': 5000, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 40, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 70}, {'per_diem': 1, 'interest': 30, 'penalty': 100, 'payoff': 8630}], ['control 1', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 115, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 100}, {'per_diem': 4228, 'interest': 63420, 'penalty': 0, 'payoff': 12412598}], ['control 2', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 130}, {'per_diem': 12, 'interest': 12, 'penalty': 2000, 'payoff': 105512}], ['control 3', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 61}, {'per_diem': 123, 'interest': 123, 'penalty': 10000, 'payoff': 1010122}], ['control 4', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 360, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 70}, {'per_diem': 35, 'interest': 35, 'penalty': 2000, 'payoff': 90035}], ['control 5', {'balance': 5000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 100, 'penalty_until': 100}, {'per_diem': 1, 'interest': 1, 'penalty': 0, 'payoff': -6999}], ['control 6', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 360, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 16}, {'per_diem': 35, 'interest': 35, 'penalty': 0, 'payoff': 91535}]], [['regression: per diem rounding stage', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 131, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 115}, {'per_diem': 347, 'interest': 10757, 'penalty': 0, 'payoff': 1014256}], ['regression: per diem rounding stage, partial-repair probe', {'balance': 999999, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 40, 'basis': 360, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 0, 'penalty_until': 70}, {'per_diem': 167, 'interest': 5010, 'penalty': 0, 'payoff': 1005009}], ['control 1', {'balance': 12345678, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 100, 'penalty_until': 130}, {'per_diem': 1522, 'interest': 1522, 'penalty': 123457, 'payoff': 12478157}], ['control 2', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 31, 'basis': 360, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 200, 'penalty_until': 16}, {'per_diem': 125, 'interest': 3750, 'penalty': 0, 'payoff': 1007749}], ['control 3', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 25}, {'per_diem': 123, 'interest': 123, 'penalty': 0, 'payoff': 991622}], ['control 4', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 16}, {'per_diem': 34, 'interest': 34, 'penalty': 0, 'payoff': 104034}], ['control 5', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 61}, {'per_diem': 123, 'interest': 123, 'penalty': 0, 'payoff': 1007622}]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: per diem rounding stage	`{'interest': 750, 'payoff': 108250, 'penalty': 0, 'per_diem': 17}`	`{'interest': 765, 'payoff': 108265, 'penalty': 0, 'per_diem': 17}`	Failed
control 1	`{'interest': 164, 'payoff': 1000163, 'penalty': 0, 'per_diem': 164}`	`{'interest': 164, 'payoff': 1000163, 'penalty': 0, 'per_diem': 164}`	Passed
control 2	`{'interest': 2029, 'payoff': 12598121, 'penalty': 246914, 'per_diem': 2029}`	`{'interest': 2029, 'payoff': 12598121, 'penalty': 246914, 'per_diem': 2029}`	Passed
control 3	`{'interest': 347, 'payoff': 1011846, 'penalty': 20000, 'per_diem': 347}`	`{'interest': 347, 'payoff': 1011846, 'penalty': 20000, 'per_diem': 347}`	Passed
control 4	`{'interest': 2058, 'payoff': 12582650, 'penalty': 246914, 'per_diem': 2058}`	`{'interest': 2058, 'payoff': 12582650, 'penalty': 246914, 'per_diem': 2058}`	Passed
control 5	`{'interest': 12, 'payoff': 103512, 'penalty': 0, 'per_diem': 12}`	`{'interest': 12, 'payoff': 103512, 'penalty': 0, 'per_diem': 12}`	Passed
control 6	`{'interest': 2058, 'payoff': 12598150, 'penalty': 246914, 'per_diem': 2058}`	`{'interest': 2058, 'payoff': 12598150, 'penalty': 246914, 'per_diem': 2058}`	Passed

SHA-256 / e9438e225855bae51cd519dc7608e34463d3818213fc4b86491108455957552b

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    def rnd(n, d):
        q, r = divmod(n, d)
        return q + (1 if 2 * r >= d else 0)
    per_diem = x['balance'] * x['rate_bp'] // (10000 * x['basis'])
    days = x['payoff_day'] - x['last_paid_day']
    interest = per_diem * days
    penalty = rnd(x['balance'] * x['penalty_bp'], 10000) if x['payoff_day'] <= x['penalty_until'] else 0
    payoff = x['balance'] + interest + x['fees_due'] + penalty - x['escrow']
    return {'per_diem': per_diem, 'interest': interest, 'penalty': penalty, 'payoff': payoff}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: per diem rounding stage', {'balance': 100000, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 145, 'basis': 360, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 115}, {'per_diem': 17, 'interest': 765, 'penalty': 0, 'payoff': 108265}], ['control 1', {'balance': 999999, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 10}, {'per_diem': 164, 'interest': 164, 'penalty': 0, 'payoff': 1000163}], ['control 2', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 160}, {'per_diem': 2029, 'interest': 2029, 'penalty': 246914, 'payoff': 12598121}], ['control 3', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 360, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 70}, {'per_diem': 347, 'interest': 347, 'penalty': 20000, 'payoff': 1011846}], ['control 4', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 130}, {'per_diem': 2058, 'interest': 2058, 'penalty': 246914, 'payoff': 12582650}], ['control 5', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 0, 'penalty_until': 115}, {'per_diem': 12, 'interest': 12, 'penalty': 0, 'payoff': 103512}], ['control 6', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 115}, {'per_diem': 2058, 'interest': 2058, 'penalty': 246914, 'payoff': 12598150}]], [['regression: per diem rounding stage', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 46, 'basis': 365, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 100, 'penalty_until': 1}, {'per_diem': 342, 'interest': 15390, 'penalty': 0, 'payoff': 1022889}], ['regression: per diem rounding stage, partial-repair probe', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 61}, {'per_diem': 13, 'interest': 13, 'penalty': 2000, 'payoff': 105513}], ['control 1', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 31, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 0, 'penalty_until': 61}, {'per_diem': 125, 'interest': 3750, 'penalty': 0, 'payoff': 1007249}], ['control 2', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 40}, {'per_diem': 4228, 'interest': 4228, 'penalty': 0, 'payoff': 12337906}], ['control 3', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 130}, {'per_diem': 12, 'interest': 12, 'penalty': 2000, 'payoff': 90012}], ['control 4', {'balance': 12345678, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 200, 'penalty_until': 40}, {'per_diem': 1522, 'interest': 1522, 'penalty': 246914, 'payoff': 12598114}], ['control 5', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 100}, {'per_diem': 342, 'interest': 342, 'penalty': 0, 'payoff': 1000341}]], [['regression: per diem rounding stage', {'balance': 5000, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 55, 'basis': 365, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 40}, {'per_diem': 1, 'interest': 45, 'penalty': 0, 'payoff': 9045}], ['control 1', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 100, 'penalty_until': 1}, {'per_diem': 34, 'interest': 34, 'penalty': 0, 'payoff': 91534}], ['control 2', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 100}, {'per_diem': 4287, 'interest': 4287, 'penalty': 0, 'payoff': 12337965}], ['control 3', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 40, 'basis': 360, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 100, 'penalty_until': 10}, {'per_diem': 125, 'interest': 3750, 'penalty': 0, 'payoff': 995249}], ['control 4', {'balance': 100000, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 360, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 100, 'penalty_until': 10}, {'per_diem': 17, 'interest': 17, 'penalty': 0, 'payoff': 104017}], ['control 5', {'balance': 12345678, 'rate_bp': 600, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 160}, {'per_diem': 2058, 'interest': 2058, 'penalty': 0, 'payoff': 12355236}], ['control 6', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 360, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 100}, {'per_diem': 4287, 'interest': 4287, 'penalty': 0, 'payoff': 12349965}]], [['regression: per diem rounding stage', {'balance': 5000, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 40, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 70}, {'per_diem': 1, 'interest': 30, 'penalty': 100, 'payoff': 8630}], ['control 1', {'balance': 12345678, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 115, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 100}, {'per_diem': 4228, 'interest': 63420, 'penalty': 0, 'payoff': 12412598}], ['control 2', {'balance': 100000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 200, 'penalty_until': 130}, {'per_diem': 12, 'interest': 12, 'penalty': 2000, 'payoff': 105512}], ['control 3', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 61}, {'per_diem': 123, 'interest': 123, 'penalty': 10000, 'payoff': 1010122}], ['control 4', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 360, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 200, 'penalty_until': 70}, {'per_diem': 35, 'interest': 35, 'penalty': 2000, 'payoff': 90035}], ['control 5', {'balance': 5000, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 0, 'escrow': 12000, 'penalty_bp': 100, 'penalty_until': 100}, {'per_diem': 1, 'interest': 1, 'penalty': 0, 'payoff': -6999}], ['control 6', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 360, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 16}, {'per_diem': 35, 'interest': 35, 'penalty': 0, 'payoff': 91535}]], [['regression: per diem rounding stage', {'balance': 999999, 'rate_bp': 1250, 'last_paid_day': 100, 'payoff_day': 131, 'basis': 360, 'fees_due': 3500, 'escrow': 0, 'penalty_bp': 100, 'penalty_until': 115}, {'per_diem': 347, 'interest': 10757, 'penalty': 0, 'payoff': 1014256}], ['regression: per diem rounding stage, partial-repair probe', {'balance': 999999, 'rate_bp': 600, 'last_paid_day': 10, 'payoff_day': 40, 'basis': 360, 'fees_due': 0, 'escrow': 0, 'penalty_bp': 0, 'penalty_until': 70}, {'per_diem': 167, 'interest': 5010, 'penalty': 0, 'payoff': 1005009}], ['control 1', {'balance': 12345678, 'rate_bp': 450, 'last_paid_day': 100, 'payoff_day': 101, 'basis': 365, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 100, 'penalty_until': 130}, {'per_diem': 1522, 'interest': 1522, 'penalty': 123457, 'payoff': 12478157}], ['control 2', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 31, 'basis': 360, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 200, 'penalty_until': 16}, {'per_diem': 125, 'interest': 3750, 'penalty': 0, 'payoff': 1007749}], ['control 3', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 10, 'payoff_day': 11, 'basis': 365, 'fees_due': 3500, 'escrow': 12000, 'penalty_bp': 0, 'penalty_until': 25}, {'per_diem': 123, 'interest': 123, 'penalty': 0, 'payoff': 991622}], ['control 4', {'balance': 100000, 'rate_bp': 1250, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 0, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 16}, {'per_diem': 34, 'interest': 34, 'penalty': 0, 'payoff': 104034}], ['control 5', {'balance': 999999, 'rate_bp': 450, 'last_paid_day': 1, 'payoff_day': 2, 'basis': 365, 'fees_due': 3500, 'escrow': -4000, 'penalty_bp': 0, 'penalty_until': 61}, {'per_diem': 123, 'interest': 123, 'penalty': 0, 'payoff': 1007622}]]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'raised ' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression: per diem rounding stage	`{'interest': 720, 'payoff': 108220, 'penalty': 0, 'per_diem': 16}`	`{'interest': 765, 'payoff': 108265, 'penalty': 0, 'per_diem': 17}`	Failed
control 1	`{'interest': 164, 'payoff': 1000163, 'penalty': 0, 'per_diem': 164}`	`{'interest': 164, 'payoff': 1000163, 'penalty': 0, 'per_diem': 164}`	Passed
control 2	`{'interest': 2029, 'payoff': 12598121, 'penalty': 246914, 'per_diem': 2029}`	`{'interest': 2029, 'payoff': 12598121, 'penalty': 246914, 'per_diem': 2029}`	Passed
control 3	`{'interest': 347, 'payoff': 1011846, 'penalty': 20000, 'per_diem': 347}`	`{'interest': 347, 'payoff': 1011846, 'penalty': 20000, 'per_diem': 347}`	Passed
control 4	`{'interest': 2057, 'payoff': 12582649, 'penalty': 246914, 'per_diem': 2057}`	`{'interest': 2058, 'payoff': 12582650, 'penalty': 246914, 'per_diem': 2058}`	Failed
control 5	`{'interest': 12, 'payoff': 103512, 'penalty': 0, 'per_diem': 12}`	`{'interest': 12, 'payoff': 103512, 'penalty': 0, 'per_diem': 12}`	Passed
control 6	`{'interest': 2057, 'payoff': 12598149, 'penalty': 246914, 'per_diem': 2057}`	`{'interest': 2058, 'payoff': 12598150, 'penalty': 246914, 'per_diem': 2058}`	Failed

SHA-256 / f925d22a0a524dd83d9522711310eef1a5f361d48da5494f761210796e5edefd

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 7 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic bounded teaching model with stipulated toy lending rules stated in the contract; money is integer cents and rates are basis points; it makes no claim of conformance to any regulation, servicing standard or product. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:46:28.732279+00:00.

Case digest / 6537cbbafcbb825513b24a86f8aa2a5d8e4d082fd5952153902bbac46b88a901