Added newton's method

src/newton.hpp

@@ -0,0 +1,28 @@
+#ifndef _COSMOTOOL_NEWTON_HPP
+#define _COSMOTOOL_NEWTON_HPP
+
+namespace CosmoTool
+{
+  template<typename T, typename FunT>
+  T newtonSolver(T x0, FunT function, double residual = 1e-3)
+  {
+    T x, xold = x0;
+    T f_x = function.eval(x0);
+    T df_x = function.derivative(x0);
+    
+    x = xold - f_x/df_x;
+
+    while (abs(xold-x) > residual)
+      {	
+	xold = x;
+	f_x = function.eval(x);
+	df_x = function.derivative(x);
+	x = xold - f_x/df_x;
+      }
+	   
+    return x;
+  }
+
+};
+
+#endif