下面的表是wall street Journal上的一个TIPS的报价。网址
http://online.wsj.com/mdc/public/page/2_3020-tips.html?mod=mdc_bnd_pglnk
但我没有弄明白那些负的yield是怎么计算出来的，请高人指点！谢谢！


Treasury Inflation-Protected Securities
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WHAT'S THIS?

Tuesday, November 02, 2010
Treasury Inflation-Protected Securities, or TIPS, are securities whose principal is tied to the Consumer Price Index (CPI) . The principal increases with inflation and decreases with deflation. When the security matures, the U.S. Treasury pays the original or adjusted principal, whichever is greater. TIPS pay interest every six months. Figures after periods in bid and ask quotes represent 32nds; 101.26 means 101 26/32, or 101.8125% of 100% face value; 99.01 means 99 1/32, or 99.03125% of face value.

Maturity	Coupon	Bid	Asked	Chg	Yield*	Accrued principal
2011 Jan 15	3.500	100.23	100.23	unch.	-0.131	1254
2011 Apr 15	2.375	101.02	101.02	- 1	-0.015	1099
2012 Jan 15	3.375	104.18	104.19	- 2	-0.431	1229
2012 Apr 15	2.000	103.17	103.17	- 2	-0.429	1075
2012 Jul 15	3.000	106.07	106.08	- 2	-0.645	1214
2013 Apr 15	0.625	103.09	103.10	- 2	-0.714	1032
2013 Jul 15	1.875	106.29	106.30	- 3	-0.668	1188
2014 Jan 15	2.000	108.06	108.07	- 2	-0.539	1181
2014 Apr 15	1.250	106.06	106.07	- 3	-0.535	1031
2014 Jul 15	2.000	109.10	109.11	- 3	-0.500	1158
2015 Jan 15	1.625	108.14	108.15	- 1	-0.371	1143
2015 Apr 15	0.500	104.06	104.07	- 1	-0.435	1007
2015 Jul 15	1.875	110.17	110.18	- 1	-0.349	1122
2016 Jan 15	2.000	111.16	111.17	- 2	-0.205	1099
2016 Jul 15	2.500	115.11	115.12	+ 1	-0.183	1081
2017 Jan 15	2.375	114.27	114.28	+ 3	-0.021	1082
2017 Jul 15	2.625	117.17	117.18	+ 1	0.005	1053
2018 Jan 15	1.625	110.22	110.23	+ 1	0.129	1042
2018 Jul 15	1.375	109.07	109.08	+ 1	0.165	1012
2019 Jan 15	2.125	114.30	114.31	+ 2	0.279	1016
2019 Jul 15	1.875	113.10	113.11	+ 3	0.320	1022
2020 Jan 15	1.375	108.28	108.29	+ 4	0.388	1009
2020 Jul 15	1.250	107.21	107.22	+ 5	0.441	1001
2025 Jan 15	2.375	120.03	120.04	+ 23	0.867	1158
2026 Jan 15	2.000	115.06	115.07	+ 24	0.924	1099
2027 Jan 15	2.375	121.00	121.01	+ 29	0.969	1082
2028 Jan 15	1.750	111.21	111.22	+ 30	1.009	1042
2028 Apr 15	3.625	140.04	140.05	+ 34	1.092	1349
2029 Jan 15	2.500	124.06	124.07	+ 31	1.037	1016
2029 Apr 15	3.875	146.04	146.05	+ 37	1.104	1328
2032 Apr 15	3.375	142.24	142.25	+ 43	1.125	1229
2040 Feb 15	2.125	119.01	119.02	+ 51	1.337	1010

*-Yld. to maturity on accrued principal.