Refs #9782. Changed implementation of Gaussians to not use pow

I was not aware how incredibly slow pow() is for squaring a value.
mantidproject · Aug 13, 2014 · 5e7de3e · 5e7de3e
1 parent e1440db
commit 5e7de3e
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Showing 3 changed files with 10 additions and 6 deletions.
diff --git a/Code/Mantid/Framework/CurveFitting/src/GaussianAutoDiff.cpp b/Code/Mantid/Framework/CurveFitting/src/GaussianAutoDiff.cpp
@@ -24,7 +24,8 @@ void GaussianAutoDiff::function1DAutoDiff(const FunctionDomain1D &domain, std::v
     adept::adouble sigma = parameters.getParameter("Sigma");
 
     for(size_t i = 0; i < y.size(); ++i) {
-        y[i] = height * exp(-0.5 * pow( (domain[i] - centre)/sigma, 2.0) );
+        adept::adouble term = (domain[i] - centre)/sigma;
+        y[i] = height * exp(-0.5 * term * term);
     }
 }
 

diff --git a/Code/Mantid/Framework/CurveFitting/src/GaussianHandCoded.cpp b/Code/Mantid/Framework/CurveFitting/src/GaussianHandCoded.cpp
@@ -27,7 +27,8 @@ using namespace API;
       double sigma = getParameter("Sigma");
 
       for(size_t i = 0; i < nData; ++i) {
-          out[i] = height * exp(-0.5 * pow( (xValues[i] - centre)/sigma, 2.0) );
+          double diffTerm = (xValues[i] - centre)/sigma;
+          out[i] = height * exp(-0.5 * diffTerm * diffTerm );
       }
   }
 
@@ -39,11 +40,12 @@ using namespace API;
 
       for(size_t i = 0; i < nData; ++i) {
           double xDiff = xValues[i] - centre;
-          double expTerm = exp(-0.5 * pow( (xDiff)/sigma, 2.0));
+          double term = (xDiff)/sigma;
+          double expTerm = exp(-0.5 * term * term);
 
           out->set(i, 0, expTerm);
-          out->set(i, 1, (height*expTerm*(2 * xDiff))/(2*pow(sigma, 2)));
-          out->set(i, 2, (height*expTerm*pow(xDiff, 2))/pow(sigma, 3));
+          out->set(i, 1, (height*expTerm*(xDiff))/(sigma * sigma));
+          out->set(i, 2, (height*expTerm*term * term)/(sigma));
       }
   }
 

diff --git a/Code/Mantid/Framework/CurveFitting/src/GaussianNumDiff.cpp b/Code/Mantid/Framework/CurveFitting/src/GaussianNumDiff.cpp
@@ -27,7 +27,8 @@ namespace CurveFitting
       double sigma = getParameter("Sigma");
 
       for(size_t i = 0; i < nData; ++i) {
-          out[i] = height * exp(-0.5 * pow( (xValues[i] - centre)/sigma, 2.0) );
+          double term = (xValues[i] - centre)/sigma;
+          out[i] = height * exp(-0.5 * term * term );
       }
   }