Add a couple of numerical checks.

lisitsyn#53 (comment)
Obviously, this is not to merge.

include/tapkee/methods.hpp

@@ -154,6 +154,11 @@ class ImplementationBase
         Neighbors neighbors = findNeighborsWith(kernel_distance);
         SparseWeightMatrix weight_matrix =
             linear_weight_matrix(begin, end, neighbors, kernel, parameters[nullspace_shift], parameters[klle_shift]);
+        for (int k = 0; k < weight_matrix.outerSize(); ++k) {
+            for (Eigen::SparseMatrix<double>::InnerIterator it(weight_matrix, k); it; ++it) {
+                assert(std::isfinite(it.value()));
+            }
+        }
         DenseMatrix embedding = eigendecomposition(parameters[eigen_method], parameters[computation_strategy], SmallestEigenvalues,
                                                    weight_matrix, parameters[target_dimension])
                                     .first;

include/tapkee/neighbors/neighbors.hpp

@@ -15,6 +15,7 @@
 /* End of Tapkee includes */
 
 #include <algorithm>
+#include <cmath>
 #include <utility>
 #include <vector>
 
@@ -195,6 +196,14 @@ Neighbors find_neighbors(NeighborsMethod method, const RandomAccessIterator& beg
         if (!is_connected(begin, end, neighbors))
             LoggingSingleton::instance().message_warning("The neighborhood graph is not connected.");
     }
+    int min_element = 10000000, max_element = -1;
+    for (auto const& neighbor : neighbors) {
+        for (auto const& item : neighbor) {
+            assert(std::isfinite(item));
+            min_element = std::min(min_element, item);
+            max_element = std::max(max_element, item);
+        }
+    }
     return neighbors;
 }