current exposure for a counterparty [推广有奖]

current exposure is the sum of the current values of each derivative contract adjusted for any legally binding risk reduction instruments.current exposure represents the cost for a firm to replace contracts with counterparties that default on thei obligations.the current exposure to counterparties is calculated as follows:

CEC=sigmamax(mvd.0)+sigmmax(sigmamvdb,0)

既然当前暴露是单个衍生合约考虑风险减少工具的当前价值的总和。那么上面的公式不是重复计算当前暴露了么。应该是sigmmax(sigmamvdb,0)才对啊，而且考虑netting，collateral等当前的风险暴露要比没有master agreement 小才对。

还有credit value adjustments指的是什么那？