Thank you very much! I tried to find the commonality among the missing values but it seems that there is no regular pattern... I think it should be the problem that you mentioned about the passing value. Because when I plus a tiny amount to the coupon parameter, my code runs well. (I don't know why but it did make my code work. And I checked the results, they are right because the modified parameters are extremely close to the original value). Now my problem has been solved, thank you so much for your help!
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