Re-weighing assets

Pools can be re-weighed to adjust the composition of the current desired tokens in the pool. The current desired tokens are the underlying tokens in the pool with a target weight greater than zero. Re-weighing a pool adjusts the target weights of each asset but does not remove or add tokens.

Re-indexing assets

Pools can be re-indexed to adjust both the underlying tokens and their target weights.

Any current underlying tokens which are not assigned a new target weight in the re-index call will be assigned a target weight of 0 so that they can be gradually removed from the pool. If this occurs for a token which is bound but not initialized, the token will be unbound (see unbound token handling).

New tokens added to the pool must be assigned a minimum balance which is roughly equal to 1% of the total pool value (see bootstrapping new tokens) .

Weight Adjustment

In order to rebalance through internal swaps, Indexed uses a desired weight ($D_t$) parameter which defines the target weight for an asset. If a desired weight is higher than the actual weight, the pool should increase its balance in that token. If the desired weight is lower than the actual weight, the pool should decrease its balance in that token.

Each pool has a minimum update delay, which by default is 30 minutes, and a weight change factor, which by default is 1%.

If a token with a positive weight difference ($D_t > W_t$) is swapped into the pool and it has been more than the minimum delay period since its last weight change, the pool will increase that token's weight by either the weight change factor or the token's desired weight, whichever is less.

const weightChangeFactor = 0.01;
​
updateWeightIn(tokenIn) {
  if (tokenIn.desiredWeight > tokenIn.weight) {
    tokenIn.weight = Math.min(
      tokenIn.desiredWeight,
      tokenIn.weight * (1 + weightChangeFactor)
    )
  }
}

If a token with a negative weight difference ($D_t < W_t$) is swapped out of the pool and it has been more than the minimum delay period since its last weight change, the pool will decrease that token's weight by either the weight change factor or the token's desired weight, whichever is less.

const weightChangeFactor = 0.01;
​
updateWeightOut(tokenOut) {
  if (tokenOut.desiredWeight < tokenOut.weight) {
    tokenOut.weight = Math.max(
      tokenOut.desiredWeight,
      tokenOut.weight * (1 - weightChangeFactor)
    )
  }
}

As swaps are executed and LP tokens are minted and burned, inbound tokens with desired weight increases (desired > real) and outbound tokens with desired weight decreases (real > desired) automatically adjust their weights, occasionally creating small arbitrage opportunities which move tokens toward their target balances when traders execute on them, thus rebalancing the pool.

Note: There are two exceptions to the stated weight adjustment rule:

1. The exitPool function, which sends out some amount of every initialized token. In order to minimize gas expenditure, this function does not adjust the weights of outbound tokens.

2. When an uninitialized token becomes ready, the weight can increase beyond the fee factor1.