diff --git a/eo/contrib/mathsym/GNUmakefile b/eo/contrib/mathsym/GNUmakefile
index 1e30a61a..7da7683d 100644
--- a/eo/contrib/mathsym/GNUmakefile
+++ b/eo/contrib/mathsym/GNUmakefile
@@ -1,5 +1,5 @@
 COMPILEFLAGS=-Wno-deprecated -g -Wall -Wshadow #-DINTERVAL_DEBUG
-OPTFLAGS= -O2 -DNDEBUG 
+OPTFLAGS= -O3 -DNDEBUG 
 
 PROFILE_FLAGS=-pg
 
@@ -18,7 +18,7 @@ CXXSOURCES=FunDef.cpp Sym.cpp SymImpl.cpp SymOps.cpp sym_compile.cpp TreeBuilder
 	Dataset.cpp ErrorMeasure.cpp Scaling.cpp TargetInfo.cpp BoundsCheck.cpp util.cpp NodeSelector.cpp\
 	eoSymCrossover.cpp sym_operations.cpp eoSymMutate.cpp
 
-TESTPROGRAMS=test/test_compile test/testeo test/test_simplify
+TESTPROGRAMS=test/test_compile test/testeo test/test_simplify test/test_diff
 
 OBJS= $(CXXSOURCES:.cpp=.o) c_compile.o
 
@@ -50,6 +50,9 @@ test/testeo: test/testeo.o ${SYMLIB}
 test/test_simplify: test/test_simplify.o $(SYMLIB)
 	$(CXX) -o test/test_simplify test/test_simplify.o  $(SYMLIB) ${LIBS}
 
+test/test_diff: test/test_diff.o $(SYMLIB)
+	$(CXX) -o test/test_diff test/test_diff.o  $(SYMLIB) ${LIBS}
+
 # eo
 ../../src/libeo.a:
 	make -C ../../src
diff --git a/eo/contrib/mathsym/eo_interface/eoSymEval.h b/eo/contrib/mathsym/eo_interface/eoSymEval.h
index bbc8392a..66dbcc01 100644
--- a/eo/contrib/mathsym/eo_interface/eoSymEval.h
+++ b/eo/contrib/mathsym/eo_interface/eoSymEval.h
@@ -29,13 +29,14 @@ class eoSymPopEval : public eoPopEvalFunc<EoType> {
 
     BoundsCheck&  check;
     ErrorMeasure& measure;
+    unsigned size_cap; 
     
     public:
 
-    eoSymPopEval(BoundsCheck& _check, ErrorMeasure& _measure) :
-	check(_check), measure(_measure) {}
+    eoSymPopEval(BoundsCheck& _check, ErrorMeasure& _measure, unsigned _size_cap) :
+	check(_check), measure(_measure), size_cap(_size_cap) {}
 
-    /** apparently this thing works on two populations, why?
+    /** apparently this thing works on two populations, 
      *
      * In any case, currently only implemented the population wide
      * evaluation version, as that one is much faster. This because the
@@ -51,7 +52,7 @@ class eoSymPopEval : public eoPopEvalFunc<EoType> {
 	for (unsigned i = 0; i < p1.size(); ++i) {
 	    if (p1[i].invalid()) {
 
-		if (check.in_bounds(p1[i])) {
+		if (p1[i].size() < size_cap && check.in_bounds(p1[i])) {
 		    unevaluated.push_back(i);
 		    tmppop.push_back( static_cast<Sym>(p1[i]) );
 		} else {
@@ -63,7 +64,7 @@ class eoSymPopEval : public eoPopEvalFunc<EoType> {
 	for (unsigned i = 0; i < p2.size(); ++i) {
 	    if (p2[i].invalid()) {
 		
-		if (check.in_bounds(p2[i])) {
+		if (p2[i].size() < size_cap && check.in_bounds(p2[i])) {
 		    
 		    unevaluated.push_back(p1.size() + i);
 		    tmppop.push_back( static_cast<Sym>(p2[i]) );
diff --git a/eo/contrib/mathsym/eo_interface/eoSymMutate.cpp b/eo/contrib/mathsym/eo_interface/eoSymMutate.cpp
index 49cc3b28..21e74671 100644
--- a/eo/contrib/mathsym/eo_interface/eoSymMutate.cpp
+++ b/eo/contrib/mathsym/eo_interface/eoSymMutate.cpp
@@ -54,7 +54,6 @@ bool mutate(Sym& sym, double p, const LanguageTable& table) {
 
 
 bool mutate_constants(Sym& sym, double stdev) {
-    
     vector<double> values = get_constants(sym);
 
     if (values.empty()) {
diff --git a/eo/contrib/mathsym/eo_interface/eoSymMutate.h b/eo/contrib/mathsym/eo_interface/eoSymMutate.h
index e1f9b620..33623a12 100644
--- a/eo/contrib/mathsym/eo_interface/eoSymMutate.h
+++ b/eo/contrib/mathsym/eo_interface/eoSymMutate.h
@@ -29,7 +29,6 @@ class eoSymSubtreeMutate : public eoMonOp<EoType> {
     
 	TreeBuilder& subtree_builder;
 	NodeSelector& node_selector;
-    
     public :
 	
 	eoSymSubtreeMutate(TreeBuilder& _subtree_builder, NodeSelector& _node_selector)
diff --git a/eo/contrib/mathsym/eval/sym_compile.cpp b/eo/contrib/mathsym/eval/sym_compile.cpp
index 6351d716..da491dbe 100644
--- a/eo/contrib/mathsym/eval/sym_compile.cpp
+++ b/eo/contrib/mathsym/eval/sym_compile.cpp
@@ -75,7 +75,9 @@ void write_entry(Sym sym, ostream& os, HashMap& map, unsigned out) {
 
 multi_function compile(const std::vector<Sym>& syms) {
     
-    ostringstream os;
+    // static stream to avoid fragmentation of these LARGE strings
+    static ostringstream os;
+    os.str("");
 
     os << make_prototypes();
 
@@ -88,11 +90,8 @@ multi_function compile(const std::vector<Sym>& syms) {
     }
     
     os << ";}";
-    string func_str = os.str();
-  
-    //cout << "compiling " << func_str << endl;
-    
-    return (multi_function) symc_make(func_str.c_str(), "func"); 
+ 
+    return (multi_function) symc_make(os.str().c_str(), "func"); 
 }
 
 single_function compile(Sym sym) {
@@ -140,7 +139,9 @@ string print_code(Sym sym, HashMap& map) {
 void compile(const std::vector<Sym>& syms, std::vector<single_function>& functions) {
     symc_init();
     
-    ostringstream os;
+    static ostringstream os;
+    os.str("");
+    
     os << make_prototypes();
     HashMap map; 
     for (unsigned i = 0; i < syms.size(); ++i) {
@@ -153,10 +154,11 @@ void compile(const std::vector<Sym>& syms, std::vector<single_function>& functio
 	//cout << "compiling " << os.str() << endl;	
     }
 
+    os << ends;
 #ifdef INTERVAL_DEBUG
     //cout << "Compiling " << os.str() << endl;
 #endif
-    
+
     symc_compile(os.str().c_str()); 
     symc_link();
 
diff --git a/eo/contrib/mathsym/fun/FunDef.cpp b/eo/contrib/mathsym/fun/FunDef.cpp
index 9c1bfa7f..e6290bef 100644
--- a/eo/contrib/mathsym/fun/FunDef.cpp
+++ b/eo/contrib/mathsym/fun/FunDef.cpp
@@ -482,6 +482,12 @@ string prototypes = "double pow(double, double);";
 string get_prototypes() { return prototypes; }
 unsigned add_prototype(string str) { prototypes += string("double ") + str + "(double);"; return prototypes.size(); }
 
+token_t add_function(FunDef* function, token_t where) {
+    if (language.size() <= where) language.resize(where+1);
+    language[where] = function;
+    return 0;
+}
+
 
 #define FUNCDEF(funcname) struct funcname##_struct { \
     double operator()(double val) const { return funcname(val); }\
@@ -489,20 +495,18 @@ unsigned add_prototype(string str) { prototypes += string("double ") + str + "(d
     Interval operator()(Interval val) const { return funcname(val); }\
     string name() const { return string(#funcname); }\
 };\
-const token_t funcname##_token = add_function( new Unary<funcname##_struct>);\
+static const token_t funcname##_token_static = add_function( new Unary<funcname##_struct>, funcname##_token);\
 unsigned funcname##_size = add_prototype(#funcname);
 
-
-
 FunDef* make_var(int idx) { return new Var(idx); }
 FunDef* make_const(double value) { return new Const(value); }
 
-const token_t sum_token  = add_function( new Sum );
-const token_t prod_token = add_function( new Prod);
-const token_t inv_token  = add_function( new Unary<Inv>);
-const token_t min_token  = add_function( new Unary<Min>);
-const token_t pow_token  = add_function( new Power);
-const token_t ifltz_token = add_function( new IsNeg);
+static token_t ssum_token  = add_function( new Sum , sum_token);
+static token_t sprod_token = add_function( new Prod, prod_token);
+static token_t sinv_token  = add_function( new Unary<Inv>, inv_token);
+static token_t smin_token  = add_function( new Unary<Min>, min_token);
+static token_t spow_token  = add_function( new Power, pow_token);
+static token_t sifltz_token = add_function( new IsNeg, ifltz_token);
 
 FUNCDEF(sin);
 FUNCDEF(cos);
diff --git a/eo/contrib/mathsym/fun/FunDef.h b/eo/contrib/mathsym/fun/FunDef.h
index 6fa1c248..9c722098 100644
--- a/eo/contrib/mathsym/fun/FunDef.h
+++ b/eo/contrib/mathsym/fun/FunDef.h
@@ -88,25 +88,36 @@ extern Sym SymVar(unsigned idx);
 /** simplifies a sym (sym_operations.cpp) */
 extern Sym simplify(Sym sym);
 
-/** differentiates a sym to a token (sym_operations.cpp) */
-extern Sym differentiate(Sym sym, token_t var_token);
+/** differentiates a sym to a token (sym_operations.cpp)
+ * The token can be a variable or a constant 
+*/
+extern Sym differentiate(Sym sym, token_t dx);
+struct differentiation_error{}; // thrown in case of ifltz
 
 /* Add function to the language table (and take a guess at the arity) */
 class LanguageTable;
 extern void add_function_to_table(LanguageTable& table, token_t token);
 
-// token names
-extern const token_t sum_token;
-extern const token_t prod_token;
-extern const token_t inv_token;
-extern const token_t min_token;
-extern const token_t pow_token;
-extern const token_t ifltz_token;
+enum {
+    sum_token,
+    prod_token,
+    inv_token,
+    min_token,
+    pow_token,
+    ifltz_token,
+    sin_token, cos_token, tan_token,
+    asin_token, acos_token, atan_token,
+    sinh_token, cosh_token, tanh_token,
+    acosh_token, asinh_token, atanh_token,
+    exp_token, log_token,
+    sqr_token, sqrt_token
+};
 
-#define HEADERFUNC(name) extern const token_t name##_token;\
-    inline Sym name(Sym arg) { return Sym(name##_token, arg); }
+
+#define HEADERFUNC(name) inline Sym name(Sym arg) { return Sym(name##_token, arg); }
 
 /* This defines the tokens: sin_token, cos_token, etc. */
+HEADERFUNC(inv);
 HEADERFUNC(sin);
 HEADERFUNC(cos);
 HEADERFUNC(tan);
diff --git a/eo/contrib/mathsym/fun/sym_operations.cpp b/eo/contrib/mathsym/fun/sym_operations.cpp
index dba1de30..93701d99 100644
--- a/eo/contrib/mathsym/fun/sym_operations.cpp
+++ b/eo/contrib/mathsym/fun/sym_operations.cpp
@@ -74,3 +74,100 @@ Sym simplify(Sym sym) {
     
 }
 
+Sym derivative(token_t token, Sym x) {
+    Sym one = Sym(prod_token);
+    
+    switch (token) {
+	case inv_token : return Sym(inv_token, sqr(x));
+	
+	case sin_token : return -cos(x);
+	case cos_token : return sin(x);
+	case tan_token : return one + sqr(tan(x));
+			 
+	case asin_token : return inv( sqrt(one - sqr(x)));
+	case acos_token:  return -inv( sqrt(one - sqr(x)));
+	case atan_token : return inv( sqrt(one + sqr(x)));
+	
+	case cosh_token : return -sinh(x);
+	case sinh_token : return cosh(x);
+	case tanh_token : return one - sqr( tanh(x) );
+	
+	case asinh_token : return inv( sqrt( one + sqr(x) ));
+	case acosh_token : return inv( sqrt(x-one) * sqrt(x + one)  );
+	case atanh_token : return inv(one - sqr(x));
+			 
+	case exp_token : return exp(x);
+	case log_token : return inv(x);
+
+	case sqr_token : return SymConst(2.0) * x;
+	case sqrt_token : return SymConst(0.5) * inv( sqrt(x));
+    }
+    
+    throw differentiation_error();
+    return x;
+}
+
+extern Sym differentiate(Sym sym, token_t dx) {
+    
+    token_t token = sym.token();
+    
+    Sym zero = Sym(sum_token);
+    Sym one  = Sym(prod_token);
+    
+    if (token == dx) {
+	return one;
+    }
+    
+    SymVec args = sym.args();
+
+    if (args.size() == 0) { // df/dx with f != x
+	return zero;
+    }
+    
+    switch (token) {
+	
+	case sum_token: 
+	    {
+		for (unsigned i = 0; i < args.size(); ++i) {
+		    args[i] = differentiate(args[i], dx);
+		}
+
+		if (args.size() == 1) return args[0];
+		return Sym(sum_token, args);
+	    }
+	case min_token : 
+	    {
+		return -differentiate(args[0],dx);
+	    }
+	case prod_token: 
+	    {
+		if (args.size() == 1) return differentiate(args[0], dx);
+		
+		if (args.size() == 2) {
+		    return args[0] * differentiate(args[1], dx) + args[1] * differentiate(args[0], dx);
+		}
+		// else 
+		Sym c = args.back();
+		args.pop_back();
+		Sym f = Sym(prod_token, args);
+		Sym df = differentiate( f, dx);
+
+		return c * df + f * differentiate(c,dx);
+	    }
+	case pow_token : 
+	    {
+		return pow(args[0], args[1]) * args[1] * inv(args[0]);
+	    }
+	case ifltz_token : 
+	    { // cannot be differentiated
+		throw differentiation_error(); // TODO define proper exception
+	    }
+	    
+	default: // unary function: apply chain rule
+	    {
+		Sym arg = args[0];
+		return derivative(token, arg) * differentiate(arg, dx);
+	    }
+    }
+    
+}
diff --git a/eo/contrib/mathsym/regression/ErrorMeasure.cpp b/eo/contrib/mathsym/regression/ErrorMeasure.cpp
index 71d659a8..968bdfef 100644
--- a/eo/contrib/mathsym/regression/ErrorMeasure.cpp
+++ b/eo/contrib/mathsym/regression/ErrorMeasure.cpp
@@ -165,7 +165,8 @@ class ErrorMeasureImpl {
 	
 		return result;
 	    }
-
+	
+	    
 	    std::vector<double> err(pop.size()); 
 	    
 	    for (unsigned i = 0; i < train_cases(); ++i) {
@@ -319,6 +320,6 @@ double ErrorMeasure::worst_performance() const {
 	return pimpl->train_info.tvar();
     }
     
-    return 1e+20; // TODO: make this general
+    return 1e+20; 
 }
 
diff --git a/eo/contrib/mathsym/symreg.cpp b/eo/contrib/mathsym/symreg.cpp
index 0416b9c6..0f29ff54 100644
--- a/eo/contrib/mathsym/symreg.cpp
+++ b/eo/contrib/mathsym/symreg.cpp
@@ -194,6 +194,13 @@ int main(int argc, char* argv[]) {
 	    't',
 	    "Population").value();
 
+    unsigned maximumSize = parser.createParam(
+	    0xffffffffu,
+	    "maximum-size",
+	    "Maximum size after crossover",
+	    's',
+	    "Population").value();
+    
     unsigned meas_param = parser.createParam(
 	    2u,
 	    "measure",
@@ -204,7 +211,8 @@ int main(int argc, char* argv[]) {
 		",
 		'm',
 		"Regression").value();
-   
+  
+    
     ErrorMeasure::measure meas = ErrorMeasure::mean_squared_scaled;
     if (meas_param == 0) meas = ErrorMeasure::absolute;
     if (meas_param == 1) meas = ErrorMeasure::mean_squared;
@@ -253,7 +261,7 @@ int main(int argc, char* argv[]) {
     // todo, make this parameter, etc
     double std = 0.01;
     eoSymConstantMutate<EoType> constmutate(std);
-    genetic_operator.add( constmutate, 0.1);
+    genetic_operator.add(constmutate, 0.1);
     
     eoSymNodeMutate<EoType>    nodemutate(table);
     genetic_operator.add(nodemutate, node_mut_prob);
@@ -269,7 +277,7 @@ int main(int argc, char* argv[]) {
     IntervalBoundsCheck check(dataset.input_minima(), dataset.input_maxima());
     ErrorMeasure measure(dataset, train_percentage, meas);
 
-    eoSymPopEval<EoType> evaluator(check, measure);
+    eoSymPopEval<EoType> evaluator(check, measure, maximumSize);
     
     eoDetTournamentSelect<EoType> selectOne(tournamentsize);
     eoGeneralBreeder<EoType> breeder(selectOne, genetic_operator);
diff --git a/eo/contrib/mathsym/test/test_compile.cpp b/eo/contrib/mathsym/test/test_compile.cpp
index 03efbb0b..2c2f02ae 100644
--- a/eo/contrib/mathsym/test/test_compile.cpp
+++ b/eo/contrib/mathsym/test/test_compile.cpp
@@ -17,14 +17,14 @@
 
 #include <utils/eoRNG.h>
 
-#include "FunDef.h"
-#include "sym_compile.h"
+#include <FunDef.h>
+#include <sym_compile.h>
 
-#include "Dataset.h"
-#include "ErrorMeasure.h"
-#include "LanguageTable.h"
-#include "BoundsCheck.h"
-#include "TreeBuilder.h"
+#include <Dataset.h>
+#include <ErrorMeasure.h>
+#include <LanguageTable.h>
+#include <BoundsCheck.h>
+#include <TreeBuilder.h>
 
 #include <iostream>
 
@@ -34,7 +34,7 @@ void test_xover();
 
 int main() {
     Dataset dataset;
-    dataset.load_data("problem4.dat");
+    dataset.load_data("test_data.txt");
     
     cout << "Records/Fields " << dataset.n_records() << ' ' << dataset.n_fields() << endl;
    
diff --git a/eo/contrib/mathsym/test/testeo.cpp b/eo/contrib/mathsym/test/testeo.cpp
index ef6dd3dd..8693bd16 100644
--- a/eo/contrib/mathsym/test/testeo.cpp
+++ b/eo/contrib/mathsym/test/testeo.cpp
@@ -16,17 +16,17 @@
  */
 
 
-#include "LanguageTable.h"
-#include "TreeBuilder.h"
-#include "FunDef.h"
-#include "Dataset.h"
+#include <LanguageTable.h>
+#include <TreeBuilder.h>
+#include <FunDef.h>
+#include <Dataset.h>
 
-#include "eoSymInit.h"
-#include "eoSym.h"
-#include "eoPop.h"
-#include "eoSymMutate.h"
-#include "eoSymCrossover.h"
-#include "eoSymEval.h"
+#include <eoSymInit.h>
+#include <eoSym.h>
+#include <eoPop.h>
+#include <eoSymMutate.h>
+#include <eoSymCrossover.h>
+#include <eoSymEval.h>
 
 typedef EoSym<double> EoType;
 
@@ -106,7 +106,7 @@ int main() {
     IntervalBoundsCheck check(dataset.input_minima(), dataset.input_maxima());
     ErrorMeasure measure(dataset, 0.90, ErrorMeasure::mean_squared_scaled);
 
-    eoSymPopEval<EoType> evaluator(check, measure);
+    eoSymPopEval<EoType> evaluator(check, measure, 20000);
     
     eoPop<EoType> dummy;
     evaluator(pop, dummy);