# ↪ interest rate strategy

**Implements the computation of interest rates based on the current state of the reserve. This interest rate model utilizes two distinct slopes: one applicable before reaching the `OPTIMAL_USAGE_RATIO`, and another that applies from that point up to full utilization (100%).**

Due to caching of the `PoolAddressesProvider`, an instance of this contract cannot be shared across different Hyperlend markets.

The source code is available on GitHub.

***

#### View Methods

**`getVariableRateSlope1`**

```solidity
function getVariableRateSlope1(address reserve) external view returns (uint256)
```

Provides the variable rate slope for the specified reserve when the usage ratio is below the optimal threshold. This rate is relevant when the usage ratio ranges from 0 up to `OPTIMAL_USAGE_RATIO`.

**Input Parameters:**

| Name    | Type    | Description                      |
| ------- | ------- | -------------------------------- |
| reserve | address | The address of the reserve asset |

**Return Values:**

| Type    | Description                   |
| ------- | ----------------------------- |
| uint256 | The variable rate slope value |

***

**`getVariableRateSlope2`**

```solidity
function getVariableRateSlope2(address reserve) external view returns (uint256)
```

Provides the variable rate slope for the specified reserve when the usage ratio exceeds the optimal threshold. This rate applies when the usage ratio is greater than `OPTIMAL_USAGE_RATIO`.

**Input Parameters:**

| Name    | Type    | Description                      |
| ------- | ------- | -------------------------------- |
| reserve | address | The address of the reserve asset |

**Return Values:**

| Type    | Description                   |
| ------- | ----------------------------- |
| uint256 | The variable rate slope value |

***

**`getBaseVariableBorrowRate`**

```solidity
function getBaseVariableBorrowRate(address reserve) external view override returns (uint256)
```

Returns the base variable borrow rate for the given reserve.

**Input Parameters:**

| Name    | Type    | Description                      |
| ------- | ------- | -------------------------------- |
| reserve | address | The address of the reserve asset |

**Return Values:**

| Type    | Description                           |
| ------- | ------------------------------------- |
| uint256 | The base variable borrow rate, in ray |

***

**`getMaxVariableBorrowRate`**

```solidity
function getMaxVariableBorrowRate(address reserve) external view override returns (uint256)
```

Returns the maximum variable borrow rate for the specified reserve.

**Input Parameters:**

| Name    | Type    | Description                      |
| ------- | ------- | -------------------------------- |
| reserve | address | The address of the reserve asset |

**Return Values:**

| Type    | Description                              |
| ------- | ---------------------------------------- |
| uint256 | The maximum variable borrow rate, in ray |

***

**`calculateInterestRates`**

```solidity
function calculateInterestRates(
    DataTypes.CalculateInterestRatesParams memory params
) external view override returns (uint256, uint256)
```

Calculates the interest rates based on the reserve's current state and configurations. This function returns two values: the liquidity rate and the variable borrow rate.

**Input Parameters:**

| Name   | Type                                   | Description                                   |
| ------ | -------------------------------------- | --------------------------------------------- |
| params | DataTypes.CalculateInterestRatesParams | Parameters required to compute interest rates |

The `DataTypes.CalculateInterestRatesParams` struct includes the following fields:

| Name                     | Type    | Description                                                 |
| ------------------------ | ------- | ----------------------------------------------------------- |
| unbacked                 | uint256 | The amount of unbacked tokens                               |
| liquidityAdded           | uint256 | Liquidity added during the operation                        |
| liquidityTaken           | uint256 | Liquidity withdrawn during the operation                    |
| totalDebt                | uint256 | Total amount borrowed from the reserve                      |
| reserveFactor            | uint256 | Portion of interest allocated to the market's treasury      |
| reserve                  | address | The address of the reserve                                  |
| usingVirtualBalance      | bool    | Indicates if a virtual balance is being utilized            |
| virtualUnderlyingBalance | uint256 | Virtual balance of the underlying asset for mintable assets |

**Return Values:**

| Name               | Type    | Description                                |
| ------------------ | ------- | ------------------------------------------ |
| liquidityRate      | uint256 | The liquidity rate, expressed in ray       |
| variableBorrowRate | uint256 | The variable borrow rate, expressed in ray |

***


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