Merge pull request freqtrade#11080 from stash86/docs-dca

add more explanation regarding reducing position partially

docs/strategy-callbacks.md

@@ -782,6 +782,12 @@ The strategy is expected to return a negative stake_amount (in stake currency) f
 Returning the full owned stake at that point (`-trade.stake_amount`) results in a full exit.  
 Returning a value more than the above (so remaining stake_amount would become negative) will result in the bot ignoring the signal.
 
+For a partial exit, it's important to know that the formula used to calculate the amount of the coin for the partial exit order is `amount to be exited partially = negative_stake_amount * trade.amount / trade.stake_amount`, where `negative_stake_amount` is the value returned from the `adjust_trade_position` function. As seen in the formula, the formula don't care about current profit/loss of the position. It only care about `trade.amount` and `trade.stake_amount` which aren't affected by the price movement at all.
+
+For example, let's say you buy 2 SHITCOIN/USDT at open rate of 50, which means the trade's stake amount is 100 USDT. Now the price has rose to 200 and you want to sell half of it. In that case, you have to return -50% of trade.stake_amount (0.5 * 100 USDT) which equals to -50. The bot will calculate the amount it needed to sell, which is `50 * 2 / 100` which equals 1 SHITCOIN/USDT. If you return -200 (50% of 2 * 200), the bot will ignore it since trade.stake_amount is only 100 USDT but you asked it to sell 200 USDT which means you are asking it to sell 4 SHITCOIN/USDT.
+
+Back to the example above, since current rate is 200, the current USDT value of your trade is now 400 USDT. Let's say you want to partially sell 100 USDT to take out the initial investment and leave the profit in the trade in hope of the price keep rising. In that case, you have to do different approach. First, you need to calculate the exact amount you needed to sell. In this case, since you want to sell 100 USDT worth based of current rate, the exact amount you need to partially sell is `100 * 2 / 400` which equals 0.5 SHITCOIN/USDT. Since we know now the exact amount we want to sell (0.5), the value you need to return in the `adjust_trade_position` function is `-amount to be exited partially * trade.stake_amount / trade.amount`, which equals -25. The bot will sell 0.5 SHITCOIN/USDT, keeping 1.5 in trade. You will receive 100 USDT from the partial exit.
+
 !!! Note "About stake size"
     Using fixed stake size means it will be the amount used for the first order, just like without position adjustment.
     If you wish to buy additional orders with DCA, then make sure to leave enough funds in the wallet for that.