xtfrontier lntq cfo1 lev tshr ar,tvd diff

Iteration 0: log likelihood = -226.20217 (not concave)
Iteration 1: log likelihood = 116.5455 (not concave)
Iteration 2: log likelihood = 281.07459 (not concave)
Iteration 3: log likelihood = 397.87529
Iteration 4: log likelihood = 544.83693
Iteration 5: log likelihood = 611.00851
Iteration 6: log likelihood = 684.26204 (not concave)
Iteration 7: log likelihood = 712.5007
Iteration 8: log likelihood = 756.9311
Iteration 9: log likelihood = 772.11156
Iteration 10: log likelihood = 790.88857 (not concave)
Iteration 11: log likelihood = 798.93977
Iteration 12: log likelihood = 809.44048
Iteration 13: log likelihood = 818.34935
Iteration 14: log likelihood = 823.92654 (not concave)
Iteration 15: log likelihood = 826.32391
Iteration 16: log likelihood = 828.88752
Iteration 17: log likelihood = 832.54385
Iteration 18: log likelihood = 835.05575
Iteration 19: log likelihood = 837.24069
Iteration 20: log likelihood = 837.52284
Iteration 21: log likelihood = 838.70942 (not concave)
Iteration 22: log likelihood = 838.79231
Iteration 23: log likelihood = 839.09637
Iteration 24: log likelihood = 840.36001 (not concave)
Iteration 25: log likelihood = 840.7129
Iteration 26: log likelihood = 840.74058
Iteration 27: log likelihood = 841.40736 (not concave)
Iteration 28: log likelihood = 841.41355
Iteration 29: log likelihood = 841.61156
Iteration 30: log likelihood = 841.81422
Iteration 31: log likelihood = 842.49272
Iteration 32: log likelihood = 842.91441
Iteration 33: log likelihood = 843.0115
--Break--
r(1);
是什么原因呢？我该怎么办呢？