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name: bond-spreads description: "Fixed income bond spread calculations with Bloomberg YAS parity. Implements Z-Spread, I-Spread, G-Spread, ASW (Asset Swap Spread), and OAS (Option-Adjusted Spread) for USD/EUR/GBP markets. Use when: (1) Calculating any bond spread measure, (2) Building yield curve bootstrapping, (3) Implementing spread solvers, (4) Working with post-LIBOR curves (SOFR/SONIA/€STR), (5) Bond pricing analytics, (6) Comparing spreads across methodologies, (7) Implementing Bloomberg YAS-equivalent functionality."

Bond Spread Calculations

Implements five spread methodologies for fixed income analytics with Bloomberg YAS parity and data-source neutral architecture.

Spread Hierarchy (Simplest → Most Complex)

Typical ordering: OAS ≤ Z-Spread ≈ ASW < I-Spread < G-Spread for investment-grade bonds.

Quick Reference

Z-Spread (Primary Spread)

Solve for constant Z where:

CopyP_dirty = Σ [CF_i / (1 + (s_i + Z)/2)^(2×t_i)]  // Semi-annual
P_dirty = Σ [CF_i × exp(-(s_i + Z) × t_i)]       // Continuous

Solver: Brent's method (recommended) or Newton-Raphson

• Tolerance: 1e-8 (~0.001 bp)
• Bounds: [-0.10, 1.00]
• Initial guess: YTM - benchmark_YTM

I-Spread / G-Spread

CopyI-Spread = Bond_YTM - Interpolated_Swap_Rate(maturity)
G-Spread = Bond_YTM - Interpolated_Govt_Yield(maturity)

ISDA interpolation: Linear on calendar days between bracketing tenors.

ASW (Par-Par Convention - Bloomberg Default)

CopyASW = (PV_bond_coupons_at_swap_rates - P_dirty) / PV01_annuity

OAS

Requires Hull-White model with trinomial tree or Monte Carlo. See references/spreads.md.

Currency Conventions (Post-LIBOR)

Government benchmarks: USD=Treasuries, EUR=Bunds, GBP=Gilts

Implementation Checklist

1. Curve infrastructure - Zero rates, discount factors, forward rates, par rates with interpolation
2. Day count functions - ACT/360, ACT/365F, ACT/ACT ICMA, 30/360
3. Root-finding solver - Brent's method with fallback to bisection
4. Cash flow generation - Handle settlement, ex-dividend, accrued interest

Detailed References

• Spread calculations: See references/spreads.md for formulas, solver algorithms, edge cases
• Curve construction: See references/curves.md for bootstrapping, interpolation methods
• Market conventions: See references/conventions.md for currency-specific details

Rust Data Structures

Copypub trait YieldCurve {
    fn zero_rate(&self, t: f64) -> f64;
    fn discount_factor(&self, t: f64) -> f64;
    fn forward_rate(&self, t1: f64, t2: f64) -> f64;
    fn par_rate(&self, tenor: f64) -> f64;
}

pub struct BondSpreadResult {
    pub z_spread: Option<f64>,
    pub i_spread: Option<f64>,
    pub g_spread: Option<f64>,
    pub asw_par: Option<f64>,
    pub asw_market: Option<f64>,
    pub oas: Option<f64>,
}

pub enum DayCount { Act360, Act365Fixed, ActActICMA, ActActISDA, Thirty360, ThirtyE360 }
pub enum Compounding { Simple, Annual, SemiAnnual, Quarterly, Continuous }
pub enum InterpolationMethod { Linear, LogLinear, CubicSpline, MonotoneConvex }

Validation Targets

• Roundtrip: Input swap rates must reprice exactly (< 1e-10)
• Bloomberg parity: Z-spread within ±0.05 bp, OAS within ±0.5 bp
• Arbitrage-free: Positive forwards, monotonic discount factors