Question

当我从http://nltk.googlecode.com/svn/trunk/doc/howto/classify.html尝试MaxentClassifier的示例时，我收到以下错误：

Grad eval＃0

Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    classifier = MaxentClassifier.train(train)
  File "C:\Python27\lib\site-packages\nltk\classify\maxent.py", line 323, in train
    gaussian_prior_sigma, **cutoffs)
  File "C:\Python27\lib\site-packages\nltk\classify\maxent.py", line 1456, in train_maxent_classifier_with_scipy
    model.fit(algorithm=algorithm)
  File "C:\Python27\lib\site-packages\scipy\maxentropy\maxentropy.py", line 1026, in fit
    return model.fit(self, self.K, algorithm)
  File "C:\Python27\lib\site-packages\scipy\maxentropy\maxentropy.py", line 226, in fit
    callback=callback)
  File "C:\Python27\lib\site-packages\scipy\optimize\optimize.py", line 636, in fmin_cg
    gfk = myfprime(x0)
  File "C:\Python27\lib\site-packages\scipy\optimize\optimize.py", line 176, in function_wrapper
    return function(x, *args)
  File "C:\Python27\lib\site-packages\scipy\maxentropy\maxentropy.py", line 420, in grad
    G = self.expectations() - self.K
ValueError: operands could not be broadcast together with shapes (54) (12)

Python代码：

train = [(dict(a=1,b=1,c=1), 'y'),
         (dict(a=1,b=1,c=1), 'x'),
         (dict(a=1,b=1,c=0), 'y'),
         (dict(a=0,b=1,c=1), 'x'),
         (dict(a=0,b=1,c=1), 'y'),
         (dict(a=0,b=0,c=1), 'y'),
         (dict(a=0,b=1,c=0), 'x'),
         (dict(a=0,b=0,c=0), 'x')]
test = [(dict(a=1,b=0,c=1)), # unseen
        (dict(a=1,b=0,c=0)), # unseen
        (dict(a=0,b=1,c=1)), # seen 3 times, labels=y,y,x
        (dict(a=0,b=1,c=0)) # seen 1 time, label=x
        ]
classifier = MaxentClassifier.train(train)

但我不知道如何解决它。帮助我，谢谢！

Answer 1

如果您设置算法，它会起作用：

>>> algorithm = nltk.classify.MaxentClassifier.ALGORITHMS[0]
>>> algorithm
'GIS'
>>> classifier = nltk.MaxentClassifier.train(train, algorithm)

  ==> Training (100 iterations)

      Iteration    Log Likelihood    Accuracy
      ---------------------------------------
             1          -0.69315        0.556
             2          -0.65164        0.778
             3          -0.62713        0.778
             4          -0.61084        0.667
             5          -0.59935        0.667
             6          -0.59096        0.667
            .................................
            .................................

（注意你错过了培训语料库的一行）

编辑：有几个nltk算法失败，包括'CG'。问题可能与报告here的问题相同。如果是这种情况，它可能会在nltk下一个版本中得到解决。您还可以向nltk报告错误，以帮助开发人员和您自己。

由于报道的bug似乎与numpy广播和numpy的过时使用有关，也许你可以尝试使用旧版本的numpy

当我尝试在nltk中使用MaxentClassifier的CG算法时发生ValueError

1 个答案: