在fixed income notes上看到这样一段话，求解释为什么buy options可以增加convexity，而sell options降低convexity，是用cash flow的dispersion解释么？
One way to decrease portfolio convexity is to sell calls on bonds the manager is willing to sell and sell puts on bonds that the manager is willing to receive (buy). …… (We examine increasing convexity later in this review. It should beno surprise that buying options will increase convexity.)