upgraded leastsq

src/minimal_leastsq.cc

@@ -20,37 +20,54 @@
 #include <math.h>
 
 // Internal function to calculate the different scalability forms
-double FittingCurve(double n, benchmark::BigO complexity) {
+std::function<double(int)> FittingCurve(benchmark::BigO complexity) {
   switch (complexity) {
-    case benchmark::oN:
-      return n;
-    case benchmark::oNSquared:
-      return pow(n, 2);
-    case benchmark::oNCubed:
-      return pow(n, 3);
-    case benchmark::oLogN:
-      return log2(n);
-    case benchmark::oNLogN:
-      return n * log2(n);
-    case benchmark::o1:
-    default:
-      return 1;
+  case benchmark::oN:
+    return [](int n) {return n; };
+  case benchmark::oNSquared:
+    return [](int n) {return n*n; };
+  case benchmark::oNCubed:
+    return [](int n) {return n*n*n; };
+  case benchmark::oLogN:
+    return [](int n) {return log2(n); };
+  case benchmark::oNLogN:
+    return [](int n) {return n * log2(n); };
+  case benchmark::o1:
+  default:
+    return [](int) {return 1; };
   }
 }
 
-// Internal function to find the coefficient for the high-order term in the
-// running time, by minimizing the sum of squares of relative error.
-//   - n          : Vector containing the size of the benchmark tests.
-//   - time       : Vector containing the times for the benchmark tests.
-//   - complexity : Fitting curve.
+// Internal function to to return an string for the calculated complexity
+std::string GetBigOString(benchmark::BigO complexity) {
+  switch (complexity) {
+    case benchmark::oN:
+      return "* N";
+    case benchmark::oNSquared:
+      return "* N**2";
+    case benchmark::oNCubed:
+      return "* N**3";
+    case benchmark::oLogN:
+      return "* lgN";
+    case benchmark::oNLogN:
+      return "* NlgN";
+    case benchmark::o1:
+      return "* 1";
+    default:
+      return "";
+  }
+}
+
+// Find the coefficient for the high-order term in the running time, by minimizing the sum of squares of relative error, for the fitting curve given on the lambda expresion.
+//   - n             : Vector containing the size of the benchmark tests.
+//   - time          : Vector containing the times for the benchmark tests.
+//   - fitting_curve : lambda expresion (e.g. [](int n) {return n; };).
 // For a deeper explanation on the algorithm logic, look the README file at
 // http://github.com/ismaelJimenez/Minimal-Cpp-Least-Squared-Fit
 
-LeastSq CalculateLeastSq(const std::vector<int>& n,
-                         const std::vector<double>& time,
-                         const benchmark::BigO complexity) {
-  CHECK_NE(complexity, benchmark::oAuto);
-
+LeastSq CalculateLeastSq(const std::vector<int>& n, 
+                         const std::vector<double>& time, 
+                         std::function<double(int)> fitting_curve) {
   double sigma_gn = 0;
   double sigma_gn_squared = 0;
   double sigma_time = 0;
@@ -58,7 +75,7 @@ LeastSq CalculateLeastSq(const std::vector<int>& n,
 
   // Calculate least square fitting parameter
   for (size_t i = 0; i < n.size(); ++i) {
-    double gn_i = FittingCurve(n[i], complexity);
+    double gn_i = fitting_curve(n[i]);
     sigma_gn += gn_i;
     sigma_gn_squared += gn_i * gn_i;
     sigma_time += time[i];
@@ -66,26 +83,19 @@ LeastSq CalculateLeastSq(const std::vector<int>& n,
   }
 
   LeastSq result;
-  result.complexity = complexity;
 
   // Calculate complexity.
-  // o1 is treated as an special case
-  if (complexity != benchmark::o1) {
-    result.coef = sigma_time_gn / sigma_gn_squared;
-  } else {
-    result.coef = sigma_time / n.size();
-  }
+  result.coef = sigma_time_gn / sigma_gn_squared;
 
   // Calculate RMS
   double rms = 0;
   for (size_t i = 0; i < n.size(); ++i) {
-    double fit = result.coef * FittingCurve(n[i], complexity);
+    double fit = result.coef * fitting_curve(n[i]);
     rms += pow((time[i] - fit), 2);
   }
 
-  double mean = sigma_time / n.size();
-
   // Normalized RMS by the mean of the observed values
+  double mean = sigma_time / n.size();
   result.rms = sqrt(rms / n.size()) / mean;
 
   return result;
@@ -105,24 +115,32 @@ LeastSq MinimalLeastSq(const std::vector<int>& n,
   CHECK_GE(n.size(), 2);  // Do not compute fitting curve is less than two benchmark runs are given
   CHECK_NE(complexity, benchmark::oNone);
 
+  LeastSq best_fit;
+
   if(complexity == benchmark::oAuto) {
     std::vector<benchmark::BigO> fit_curves = {
       benchmark::oLogN, benchmark::oN, benchmark::oNLogN, benchmark::oNSquared,
       benchmark::oNCubed };
 
     // Take o1 as default best fitting curve
-    LeastSq best_fit = CalculateLeastSq(n, time, benchmark::o1);
+    best_fit = CalculateLeastSq(n, time, FittingCurve(benchmark::o1));
+    best_fit.complexity = benchmark::o1;
+    best_fit.caption = GetBigOString(benchmark::o1);
 
     // Compute all possible fitting curves and stick to the best one
     for (const auto& fit : fit_curves) {
-      LeastSq current_fit = CalculateLeastSq(n, time, fit);
+      LeastSq current_fit = CalculateLeastSq(n, time, FittingCurve(fit));
       if (current_fit.rms < best_fit.rms) {
         best_fit = current_fit;
+        best_fit.complexity = fit;
+        best_fit.caption = GetBigOString(fit);
       }
     }
-
-    return best_fit;
+  } else {
+    best_fit = CalculateLeastSq(n, time, FittingCurve(complexity));
+    best_fit.complexity = complexity;
+    best_fit.caption = GetBigOString(complexity);
   }
 
-  return CalculateLeastSq(n, time, complexity);
+  return best_fit;
 }

src/minimal_leastsq.h

@@ -21,6 +21,7 @@
 #include "benchmark/benchmark_api.h"
 
 #include <vector>
+#include <functional>
 
 // This data structure will contain the result returned by MinimalLeastSq
 //   - coef        : Estimated coeficient for the high-order term as
@@ -35,11 +36,13 @@ struct LeastSq {
   LeastSq() :
     coef(0),
     rms(0),
-    complexity(benchmark::oNone) {}
+    complexity(benchmark::oNone),
+    caption("") {}
 
   double coef;
   double rms;
   benchmark::BigO complexity;
+  std::string caption;
 };
 
 // Find the coefficient for the high-order term in the running time, by
@@ -48,4 +51,18 @@ LeastSq MinimalLeastSq(const std::vector<int>& n,
                        const std::vector<double>& time,
                        const benchmark::BigO complexity = benchmark::oAuto);
 
+// This interface is currently not used from the oustide, but it has been provided 
+// for future upgrades. If in the future it is not needed to support Cxx03, then 
+// all the calculations could be upgraded to use lambdas because they are more 
+// powerful and provide a cleaner inferface than enumerators, but complete 
+// implementation with lambdas will not work for Cxx03 (e.g. lack of std::function).
+// In case lambdas are implemented, the interface would be like :
+//   -> Complexity([](int n) {return n;};)
+// and any arbitrary and valid  equation would be allowed, but the option to calculate
+// the best fit to the most common scalability curves will still be kept.
+LeastSq CalculateLeastSq(const std::vector<int>& n, 
+                         const std::vector<double>& time, 
+                         std::function<double(int)> fitting_curve);
+
+
 #endif