STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

报错
C:\Users\taytay-POI\AppData\Roaming\Python\Python36\site-packages\sklearn\linear_model_logistic.py:939: ConvergenceWarning: lbfgs failed to converge (status=1):
STOP: TOTAL NO. of ITERATIONS REACHED LIMIT.

Increase the number of iterations (max_iter) or scale the data as shown in:
https://scikit-learn.org/stable/modules/preprocessing.html.
Please also refer to the documentation for alternative solver options:
https://scikit-learn.org/stable/modules/linear_model.html#logistic-regression
extra_warning_msg=_LOGISTIC_SOLVER_CONVERGENCE_MSG)

解决办法
意思是达到限制的迭代总数，只需要增加迭代次数（最大值）或缩放数据就可以。
将代码改为（增加迭代次数）：

model = LogisticRegressionCV(multi_class='multinomial',max_iter=3000).fit(x_train, y_train)

最大迭代次数默认值为1000，把它改为3000即可。但这样会增加运行时间，等了好一会儿才运行完这一行。