Only small magnitudes, not negative numbers filtered.

AMDiS/src/VtkWriter.cc

 #include <stdio.h>
 #include <string>
 #include <fstream>
+#include <cstdlib>
 
 #include "VtkWriter.h"
 #include "DataCollector.h"
@@ -112,7 +113,7 @@ namespace AMDiS {
 	{
 	  if (*intPointIt == -2) {
 	    for (int j = 0; j < static_cast<int>(coordIt->size()); j++) {
-	      if (*valueIt < 1e-40) {
+	      if (std::abs(*valueIt) < 1e-40) {
 		file << " " << 0.0 << ::std::endl;
 	      } else {
 		file << " " << *valueIt << ::std::endl;