不存在最优值，这个与行业，产业生命周期，其余在供应链中的环节和地位都有关系。
这些都未必对，如果老人买了就想持有到期，他们关心的就是息票率，而投机者可能买入只是看空利率，当利率下降就获利了结了，那他更在乎YTM
货币掉期更多为的是不同货币之间的现金流，只用期货现货难以以预期的价格实现现金流的掉期

个人的粗浅看法，望指正

1. P/E in the long run tends to have a mean reversion pattern. If P/E is too high which means the stock is overvalued people short it and if P/E is too low which means the stock is undervalued people buy it.

P/E vary from different firms, different industries and different markets. Some firms may have a very high P/E but this does not mean it is very dangerous. Perhaps the average P/E of the market is quite high, or compared with the similar firm in the same industry, it is relatively low. Or just analyze the firm's earning itself, people think the firm may develop a good product in the future which can make much profit for it, thus support its high P/E, such as many pharmaceutical firms.

So it all depends.

2. Yield to maturity usually can not be the real return the invest get if he hold the bond to maturity, because it assumes the investors can reinvest the coupon with a constant yield which is impossible in most cases (market interest is always changing). So YTM is just used as a quotation. People do not talk about the price of the bonds when trading, but just the YTM. e.g. how much is the US 10-yr treasury bond? 2.6%. Different return has their different roles. Well in my opinion, they care more about the duration, especially the dollar duration. People actually buy bond to manage interest risk or speculate on the change in the interest rate. (the same as speculate the price change in the stock price), so they care more about how much they can make if there is a change in the interest rate.

3. Swap is nothing, but a series of forward contracts.

best,

As for the first issue, according to your arguments,could I derive the conclusions as follows? The P/E value of a firm is associated with the industy to which it belongs,the firm's scale ,the development stage and so on.Consequently,it is obviously wrong that the higher the P/E value,the better the firm.Nonetheless,in one sense,the higher value does reflect some good charactoristics such as the precious growth  opportunity the investors expect.So ,to some degree,it makes sense to compare different P/E values. For instance,suppose that there exist two same firms ,which has exactly the same cost functions,the same productivities and so on but for the growth opportunities.The market will expect the firm that harbours a better growth  potential has a higher P/E value.

As for the second question, in my humble opinion, the investors should not only care about the duration but the holding period yield. Firstly,assume that the investors face the interest rate risk, admittedly,we do pay attention to the bond duration because it demonstrates the interest rate elasticity of the bond and it suggests the capital loss.However, the duration or the dollar duration ignores the income of the coupons.In fact,the investors of the bonds have two part of income:the capital gain(loss)and the coupon income .In consequence,the investors should attach importance to the two parts of income if the investors'aim is to maximize their' return at the given risk. As it is, we can imagine that the money is sure to flow to some place where the money can get more return.So no matter what financial products you decide to choose,the only thing you must deliberate thoroughly is that which return is more higher. The holding period return is the very return that encompasses all income you can get .But the HPR has a lethal defect: it is an ex post return by which you can evaluate your investment ,but you cannot use it to choose the financial products because the HPR is considerably uncertain.COnsequently,before investment ,priorities should be given to the duration and the coupon rate.BUt when it comes to evaluates your investment,the HPR is undoubtedly an effective instrument.

1. Sure. The answer is open.

2. I think you misunderstand my point. I just say they care " more" instead of they only care. What you said is correct, coupon is just like the divided in stock. My point is that to a certain extent coupon is a " disaster" to bond investors. Because you do not know the future interest rate, managing coupon is a tough task.  In, general, I agree with your point. I just mean, in many cases, bond is also invested as an interest derivative, not just a source of fixed cash flow.
To directly answer you question, yield to maturity is more commonly considered.

Best,

I get your point,thanks for your help!