git commit: [SPARK-2552][MLLIB] stabilize logistic function in pyspark

[me...@apache.org]

Repository: spark
Updated Branches:
  refs/heads/master 9564f8548 -> b86db517b


[SPARK-2552][MLLIB] stabilize logistic function in pyspark

to avoid overflow in `exp(x)` if `x` is large.

Author: Xiangrui Meng <me...@databricks.com>

Closes #1493 from mengxr/py-logistic and squashes the following commits:

259e863 [Xiangrui Meng] stabilize logistic function in pyspark


Project: http://git-wip-us.apache.org/repos/asf/spark/repo
Commit: http://git-wip-us.apache.org/repos/asf/spark/commit/b86db517
Tree: http://git-wip-us.apache.org/repos/asf/spark/tree/b86db517
Diff: http://git-wip-us.apache.org/repos/asf/spark/diff/b86db517

Branch: refs/heads/master
Commit: b86db517b6a2795f687211205b6a14c8685873eb
Parents: 9564f85
Author: Xiangrui Meng <me...@databricks.com>
Authored: Sun Jul 20 18:40:36 2014 -0700
Committer: Xiangrui Meng <me...@databricks.com>
Committed: Sun Jul 20 18:40:36 2014 -0700

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 python/pyspark/mllib/classification.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
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http://git-wip-us.apache.org/repos/asf/spark/blob/b86db517/python/pyspark/mllib/classification.py
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diff --git a/python/pyspark/mllib/classification.py b/python/pyspark/mllib/classification.py
index 1c0c536..9e28dfb 100644
--- a/python/pyspark/mllib/classification.py
+++ b/python/pyspark/mllib/classification.py
@@ -63,7 +63,10 @@ class LogisticRegressionModel(LinearModel):
     def predict(self, x):
         _linear_predictor_typecheck(x, self._coeff)
         margin = _dot(x, self._coeff) + self._intercept
-        prob = 1/(1 + exp(-margin))
+        if margin > 0:
+            prob = 1 / (1 + exp(-margin))
+        else:
+            prob = 1 - 1 / (1 + exp(margin))
         return 1 if prob > 0.5 else 0