Warning: Number of instruments may be large relative to number of observations.
Warning: Two-step estimated covariance matrix of moments is singular.
  Using a generalized inverse to calculate robust weighting matrix for Hansen test.
  Difference-in-Sargan/Hansen statistics may be negative.

求教如题：请教如何调整？
1.如何来有效减少工具变量的个数？
2.我用的是one-step，怎么提示two-step的问题？
初学，请高手指教。