Adaptive Linear Kink IRM

In the Adaptive Linear Kink IRM, the IRM hyperparameters update during each query of the borrow rate, so that the hyperparameters gradually update and don't require manual maintenance.

Features

• Optional gracePeriod in seconds for markets

• Optional minimum interactionCount number of interactions for seeding protections

struct AdaptiveConfig {
    uint256 targetUtilization; // Target utilization (in wad, e.g., 0.8e18 for 80%)
    uint256 initialRateAtTarget; // Starting rate at target utilization (in wad per second)
    uint256 minRateAtTarget; // Minimum rate at target utilization (in wad per second)
    uint256 maxRateAtTarget; // Maximum rate at target utilization (in wad per second)
    uint256 adjustmentSpeed; // Speed of adaptation (in wad per second)
    uint256 curveParameter; // Controls curve steepness (in wad, e.g., 2e18 for 2x)
    uint48 gracePeriod; // Grace period for new markets (in seconds)
    uint48 minUpdateInterval; // Minimum time between updates (in seconds)
    uint256 maxRateChange; // Maximum rate change per update (in wad, e.g., 0.1e18 for 10%)
}

/// @notice Current adaptive state for a specific market tranche.
struct AdaptiveState {
    uint128 rateAtTarget; // Current adaptive rate at target utilization
    uint64 lastUtilization; // Previous utilization for trend analysis
    uint48 lastUpdate; // Timestamp of last update
    uint48 creationTime; // Market creation timestamp for grace period
    uint16 interactionCount; // Number of interactions (for seeding protection)
}

function getTrancheBorrowRate(Id marketId, uint256 trancheIndex, uint256 trancheUtilization, bytes calldata)
    external
    override(BaseLinearKinkIrm, IIrm)
    returns (uint256 trancheBorrowRate)
{
    // Always update adaptive state (unless paused)
    if (!adaptationPaused[marketId]) {
        _updateAdaptiveState(marketId, trancheIndex, trancheUtilization);
    }

    // Calculate rate using the (possibly updated) stored state
    IBaseLinearKinkIrm.TrancheRateConfig memory rateConfig = _getTrancheRateConfig(marketId, trancheIndex);
    return _calculatePiecewiseRate(rateConfig, trancheUtilization);
}