Liquidity.Party/lmsr-amm
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pure kappa formulation: target slippage extracted into pool creator code

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tim
2025-09-23 19:08:14 -04:00
parent cd663105f4
commit b5eab7dad1
8 changed files with 198 additions and 290 deletions
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23
src/PartyPool.sol
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@@ -49,12 +49,10 @@ contract PartyPool is IPartyPool, ERC20, ReentrancyGuard {
// priced the same. This target is actually a minimum slippage that the pool imposes on traders, and the actual
// slippage cost can be multiples bigger in practice due to pool inventory imbalances.
/// @notice Trade fraction (Q64.64) representing a reference trade size as fraction of one asset's inventory.
/// @dev Used by the LMSR stabilization logic to compute target slippage.
int128 public immutable tradeFrac; // slippage target trade size as a fraction of one asset's inventory
/// @notice Target slippage (Q64.64) applied for the reference trade size specified by tradeFrac.
int128 public immutable targetSlippage; // target slippage applied to that trade size
/// @notice Liquidity parameter κ (Q64.64) used by the LMSR kernel: b = κ * S(q)
/// @dev Pool is constructed with a fixed κ. Clients that previously passed tradeFrac/targetSlippage
/// should use LMSRStabilized.computeKappaFromSlippage(...) to derive κ and pass it here.
int128 public immutable kappa; // kappa in Q64.64
/// @notice Per-swap fee in parts-per-million (ppm). Fee is taken from input amounts before LMSR computations.
uint256 public immutable swapFeePpm;
@@ -94,8 +92,7 @@ contract PartyPool is IPartyPool, ERC20, ReentrancyGuard {
/// @param symbol_ LP token symbol
/// @param _tokens token addresses (n)
/// @param _bases scaling bases for each token (n) - used when converting to/from internal 64.64 amounts
/// @param _tradeFrac trade fraction in 64.64 fixed-point (as used by LMSR)
/// @param _targetSlippage target slippage in 64.64 fixed-point (as used by LMSR)
/// @param _kappa liquidity parameter κ (Q64.64) used to derive b = κ * S(q)
/// @param _swapFeePpm fee in parts-per-million, taken from swap input amounts before LMSR calculations
/// @param _flashFeePpm fee in parts-per-million, taken for flash loans
/// @param _stable if true and assets.length==2, then the optimization for 2-asset stablecoin pools is activated.
@@ -104,8 +101,7 @@ contract PartyPool is IPartyPool, ERC20, ReentrancyGuard {
string memory symbol_,
IERC20[] memory _tokens,
uint256[] memory _bases,
int128 _tradeFrac,
int128 _targetSlippage,
int128 _kappa,
uint256 _swapFeePpm,
uint256 _flashFeePpm,
bool _stable
@@ -114,8 +110,7 @@ contract PartyPool is IPartyPool, ERC20, ReentrancyGuard {
require(_tokens.length == _bases.length, "Pool: lengths mismatch");
tokens = _tokens;
bases = _bases;
tradeFrac = _tradeFrac;
targetSlippage = _targetSlippage;
kappa = _kappa;
require(_swapFeePpm < 1_000_000, "Pool: fee >= ppm");
swapFeePpm = _swapFeePpm;
require(_flashFeePpm < 1_000_000, "Pool: flash fee >= ppm");
@@ -192,8 +187,8 @@ contract PartyPool is IPartyPool, ERC20, ReentrancyGuard {
unchecked { i++; }
}
// Initialize the stabilized LMSR state
lmsr.init(newQInternal, tradeFrac, targetSlippage);
// Initialize the stabilized LMSR state with provided kappa
lmsr.init(newQInternal, kappa);
// Compute actual LP tokens to mint based on size metric (scaled)
if( lpTokens != 0 )