先了解一下yield 和rate of return的不同定義和算法就理解了

• Yield and return both measure an investment's financial value over a set period of time, but do it using different metrics.
• Yield is the amount an investment earns during a time period, usually reflected as a percentage.
• Return is how much an investment earns or loses over time, reflected as the difference in the holding's dollar value.
• The yield is forward-looking and the return is backward-looking.