> For the complete documentation index, see [llms.txt](https://docs.gooddollar.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.gooddollar.org/previous-protocol-versions/protocol-v3/core-contracts-and-api/goodmarketmaker.md).

# GoodMarketMaker

### Events

#### BalancesUpdated

Emits when a change has occurred in a reserve balance, i.e. buy / sell will change the balance.

<table><thead><tr><th width="200.9737758180553">Parameter name</th><th>Annotation</th></tr></thead><tbody><tr><td>caller</td><td>The account who initiated the action.</td></tr><tr><td>reserveToken</td><td>The address of the reserve token.</td></tr><tr><td>amount</td><td>The incoming amount.</td></tr><tr><td>returnAmount</td><td>The return value.</td></tr><tr><td>totalSupply</td><td>The updated total supply.</td></tr><tr><td>reserveBalance</td><td>The updated reserve balance.</td></tr></tbody></table>

```
event BalancesUpdated(
    address indexed caller,
    address indexed reserveToken,
    uint256 amount,
    uint256 returnAmount,
    uint256 totalSupply,
    uint256 reserveBalance
);
```

#### ReserveRatioUpdated

Emits when the ratio changed. The caller should be the Avatar by definition.

<table><thead><tr><th width="200.9737758180553">Parameter name</th><th>Annotation</th></tr></thead><tbody><tr><td>caller</td><td>The address of the staker.</td></tr><tr><td>nom</td><td>Nominator of the ratio.</td></tr><tr><td>denom</td><td>Denominator of the ratio.</td></tr></tbody></table>

```
event ReserveRatioUpdated(address indexed caller, uint256 nom, uint256 denom);
```

### calculateNewReserveRatio

Calculates how much to decrease the reserve ratio for `_token` by the `reserveRatioDailyExpansion`.

| Parameter name | Annotation                                            |
| -------------- | ----------------------------------------------------- |
| \_token        | The reserve token to calculate the reserve ratio for. |

Returns: the new reserve ratio.

```
function calculateNewReserveRatio(ERC20 _token) public view returns (uint32);
```

### buyReturn

Calculates the buy return in G$ according to the given `_tokenAmount`.

| Parameter name | Annotation                               |
| -------------- | ---------------------------------------- |
| \_token        | The reserve token buying with.           |
| \_tokenAmount  | The amount of reserve token buying with. |

Returns: A number of G$ that should be given in exchange as calculated by the bonding curve.

```
function buyReturn(ERC20 _token, uint256 _tokenAmount);
```

### sellReturn

Calculates the sell return in `_token` according to the given `_gdAmount`.

| Parameter name | Annotation                               |
| -------------- | ---------------------------------------- |
| \_token        | The reserve token buying with.           |
| \_gdAmount     | The amount of reserve token buying with. |

Returns: A number of tokens that should be given in exchange as calculated by the bonding curve.

```
function sellReturn(ERC20 _token, uint256 _gdAmount);
```

### buy

Updates the `_token` bonding curve params. Emits `BalancesUpdated` with the new reserve token information.

| Parameter name | Annotation                               |
| -------------- | ---------------------------------------- |
| \_token        | The reserve token buying with.           |
| \_tokenAmount  | The amount of reserve token buying with. |

Returns: A number of G$ that will be given in exchange as calculated by the bonding curve.

```
function buy(ERC20 _token, uint256 _tokenAmount);
```

### sellWithContribution

Calculates the sell return with contribution in `_token` and update the bonding curve params. Emits `BalancesUpdated` with the new reserve token information.

| Parameter name         | Annotation                                                             |
| ---------------------- | ---------------------------------------------------------------------- |
| \_token                | The desired reserve token to have.                                     |
| \_gdAmount             | The amount of G$ that are sold.                                        |
| \_contributionGdAmount | The number of G$ tokens that will not be traded for the reserve token. |

Returns: A number of tokens that will be given in exchange as calculated by the bonding curve.

```
function sellWithContribution(
	ERC20 _token,
	uint256 _gdAmount,
	uint256 _contributionGdAmount
) public returns (uint256);
```


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