Fix SP unstable output, synapse decay

src/nupic/algorithms/SpatialPooler.cpp

@@ -488,6 +488,16 @@ const vector<Real>& SpatialPooler::getBoostedOverlaps() const
   return boostedOverlaps_;
 }
 
+/** helper method that checks SP output is stable for given configuration */
+bool checkUnstableParams_(SpatialPooler &sp) {
+  vector<UInt> input(sp.getNumInputs(), 1); //auto size of input
+  vector<UInt> out1(sp.getNumColumns(), 0); 
+  vector<UInt> out2(sp.getNumColumns(), 0); 
+  sp.compute(input.data(), false, out1.data());
+  sp.compute(input.data(), false, out2.data());
+  return std::equal(std::begin(out1), std::end(out1), std::begin(out2)); //compare all, element wise
+}
+
 void SpatialPooler::initialize(vector<UInt> inputDimensions,
   vector<UInt> columnDimensions,
   UInt potentialRadius,
@@ -593,6 +603,9 @@ void SpatialPooler::initialize(vector<UInt> inputDimensions,
     printParameters();
     std::cout << "CPP SP seed                 = " << seed << std::endl;
   }
+
+  //check for reasonable params
+  NTA_CHECK(checkUnstableParams_(*this)); //TODO the assert runs only at debug builds, make mandatory?
 }
 
 void SpatialPooler::compute(UInt inputArray[], bool learn,

src/test/unit/algorithms/SpatialPoolerTest.cpp

@@ -24,6 +24,8 @@
  * Implementation of unit tests for SpatialPooler
  */
 
+#include <algorithm> //generate
+#include <cstdlib> //rand
 #include <cstring>
 #include <fstream>
 #include <stdio.h>
@@ -2222,6 +2224,54 @@ namespace {
     EXPECT_EQ(0, countNonzero(activeColumns));
   }
 
+
+  // function generator:
+  int RandomNumber01 () { return (rand()%2); } // returns random (binary) numbers from {0,1}
+
+  TEST(SpatialPoolerTest, testConstructorInitParamsUnstable)
+  {
+  /** this test exposes bug where c++ SP (wrongly) produces
+  different output for the same input. 
+  XXX sensitive - marks (empirically!) discovered set of parameter 
+  that produce the err behavior; changing any of the XXX params 
+  may cause the SP to behave "normally"
+  */
+  SpatialPooler sp{std::vector<UInt>{1000} /* input*/, std::vector<UInt>{20}/* SP output cols XXX sensitive*/,
+                        /*pot radius*/ 20, //each col sees
+                        /*pot pct*/ 0.5, //XXX sensitive
+                        /*global inhibition*/ false, //XXX sensitive
+                       /*Real localAreaDensity=*/0.02, //2% active cols
+                       /*UInt numActiveColumnsPerInhArea=*/0, //mutex with above ^^ //XXX sensitive
+};
+  sp.setBoostStrength(0.0); 
+
+    vector<UInt> input(sp.getNumInputs(), 1);
+   vector<UInt> out1(sp.getNumColumns(), 0);
+    vector<UInt> out2(sp.getNumColumns(), 0);
+
+  for(UInt i=0; i< 1800; i++) { //epochs
+    //burn in
+    for (UInt burnIn=1; burnIn < 90; burnIn++) {
+      generate(input.begin(), input.end(),  RandomNumber01); //random input
+      sp.compute(input.data(), true, out1.data()); //burn in
+      cout<<".";
+      cout.flush();
+    }
+
+    //compare
+    for (UInt noLearn=1; noLearn < 90; noLearn++) {
+      generate(input.begin(), input.end(),  RandomNumber01); //random input
+      sp.compute(input.data(), false, out1.data());
+      sp.compute(input.data(), false, out2.data());
+      EXPECT_EQ(out1, out2); //not necessary with the check in SP initialize(), but keep here as example
+      cout<<"=";
+      cout.flush();
+    }
+  cout<<endl;
+  }
+}
+
+
   TEST(SpatialPoolerTest, testSaveLoad)
   {
     const char* filename = "SpatialPoolerSerialization.tmp";