Function calculateWasteMetric

Description

From https://bitcoin.stackexchange.com/questions/113622/what-does-waste-metric-mean-in-the-context-of-coin-selection See also https://github.com/bitcoin/bitcoin/pull/22009 which implements the waste metric in Bitcoin Core. and https://github.com/bitcoin/bitcoin/blob/ae024137bda9fe189f4e7ccf26dbaffd44cbbeb6/src/wallet/coinselection.cpp#L827-L853

The waste metric provides a heuristic per which a wallet's automated coin selection can achieve feerate sensitive coin selection.

waste metric formula: waste = weight×(feerate-longtermfeerate)+change+excess

• weight: total weight of the input set
• feerate: the transaction's target feerate
• L: the long-term feerate estimate which the wallet might need to pay to redeem remaining UTXOs
• changeCost: the cost of creating and spending a change output
• excess: the amount by which we exceed our selection target when creating a changeless transaction, mutually exclusive with cost of change