[mlpack] Det Bug ticket #334

[Aakash Chaudhary]

the svn diff:

Index: src/mlpack/methods/det/dt_utils.cpp
===================================================================
--- src/mlpack/methods/det/dt_utils.cpp (revision 16347)
+++ src/mlpack/methods/det/dt_utils.cpp (working copy)
@@ -215,7 +215,7 @@

     // Sequentially prune with all the values of available alphas and
adding
     // values for test values.
-    for (size_t i = 0; i < prunedSequence.size() - 2; ++i)
+    for (size_t i = 0; i < ((prunedSequence.size() <= 1) ? 0 :
prunedSequence.size() - 2); ++i)
     {
       // Compute test values for this state of the tree.
       double cvVal = 0.0;
@@ -242,7 +242,7 @@
       cvVal += cvDTree->ComputeValue(testPoint);
     }

-    regularizationConstants[prunedSequence.size() - 2] += 2.0 * cvVal /
+    regularizationConstants[((prunedSequence.size() <= 1) ? 0 :
prunedSequence.size() - 2)] += 2.0 * cvVal /
         (double) dataset.n_cols;

     test.reset();



explanation
/*
the first change        ( you gave that as hint   even then i am explaining
)
the value of prunedSequence.size() - 2   becomes big when
 prunedSequence.size() = 1 or 0   (the number of nodes)

which results into for loop execution nearly infinte times
resulting into segmentation fault


now about the second change   the same thing is happening

assuming prunedSequence.size() = 1 or 0 [for other values it will work as
it used to be]

and you were saying that it might effect the output  but it wont because

at line 255 there is a for loop
for (size_t i = 0; i < prunedSequence.size() - 1; ++i)
 regularizationConstants[i]  is used in this *for loop* and wont be used
after that

and that *for loop* wont be executed because it will fail condition    i <
prunedSequence.size() - 1     (for loop condition)

and hence we don't have to be worried about what is stored in
regularizationConstants  vector




it doesnt affect the outcome of program and also will not result into
segmentation fault


i know this might not be a good explanation but just tell me what i was not
able to explain and i will try to explain that part in a better way
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