Merge pull request ipld#165 from filecoin-project/feat/block-reward-l…

…ogic

write out block reward logic

mining.md

@@ -270,7 +270,32 @@ An eligible miner broadcasts the completed block to the network (via [block prop
 
 ### Block Rewards
 
-Currently the block reward is a fixed 1000 FIL. This will change soon.
+Over the entire lifetime of the protocol, 1,400,000,000 FIL (`TotalIssuance`) will be given out to miners. The rate at which the funds are given out is set to halve every six years, smoothly (not a fixed jump like in Bitcoin). These funds are initially held by the network account actor, and are transferred to miners in blocks that they mine. The reward amount remains fixed for a period of 1 week (given our 30 second block time, this  is 20,160 blocks, the `AdjustmentPeriod`) and is then adjusted. Over time, the reward will eventually become zero as the fractional amount given out at each step shrinks the network accounts balance to 0.
+
+The equation for the current block reward is of the form:
+
+```
+Reward = IV * (Decay ^ (BlockHeight / 20160))
+```
+
+`IV` is the initial value, and is computed by taking:
+
+```
+IV = TotalIssuance * (1 - Decay)
+```
+
+`Decay` is computed by:
+
+```
+Decay = e^(ln(0.5) / (HalvingPeriodBlocks / AdjustmentPeriod))
+```
+
+```
+// Given one block every 30 seconds, this is how many blocks are in six years
+HalvingPeriodBlocks = 6 * 365 * 24 * 60 * 2
+```
+
+Note: Due to jitter in EC, and the gregorian calendar, there may be some error in the issuance schedule over time. This is expected to be small enough that it's not worth correcting for. Additionally, since the payout mechanism is transferring from the network account to the miner, there is no risk of minting *too much* FIL.
 
 ### Open Questions
 
@@ -281,4 +306,4 @@ Currently the block reward is a fixed 1000 FIL. This will change soon.
 There are many ideas for improving upon the storage miner, here are ideas that may be potentially implemented in the future.
 
 - **Sector Resealing**: Miners should be able to 're-seal' sectors, to allow them to take a set of sectors with mostly expired pieces, and combine the not-yet-expired pieces into a single (or multiple) sectors.
-- **Sector Transfer**: Miners should be able to re-delegate the responsibility of storing data to another miner. This is tricky for many reasons, and will not be implemented in the initial release of Filecoin, but could provide interesting capabilities down the road.
+- **Sector Transfer**: Miners should be able to re-delegate the responsibility of storing data to another miner. This is tricky for many reasons, and will not be implemented in the initial release of Filecoin, but could provide interesting capabilities down the road.