用Heckman二阶段模型，跑数据半天没结果，怎么办？（在线急等）
“。。。
Iteration 10835: log likelihood = -5678.4981  (not concave)
Iteration 10836: log likelihood = -5678.4981  (not concave)
Iteration 10837: log likelihood = -5678.4981  (not concave)
Iteration 10838: log likelihood = -5678.4981  (not concave)
Iteration 10839: log likelihood = -5678.4981  (not concave)
Iteration 10840: log likelihood = -5678.4981  (not concave)
。。。”
       一直显示在迭代，求牛人解答