Compute slippage

[AngelaKTE]

• slippage in % # over time, calculated based on ?
  pls add how calculate slippage in case of liquidity provision! (see above)

[VasilySumanov]

A function for computing slippage in case of single-side liquidity provision for token_amount_in (number of tokens) tokens of token_in type - slippage_in:

1. Calculate the lp_token_value_in by multiplying token_amount_in on current ?USD price of token_in type
2. Call join_swap_extern_amount_in with token_in and token_amount_in input parameters.
   The function will return pool_amount_out, which is defined as lp_pool_out in our Naming Convention
3. Calculate the current value of received BPT Tokens lp_pool_value using the algorithm presented in Issue 3
4. The absolute slippage in decimal: (lp_token_value_in - lp_pool_value)/lp_token_value_in