added code

Author: mhjensen

doc/Programs/LecturePrograms/programs/IntroProgramming/cpp/derivative.cpp

@@ -12,7 +12,7 @@ std::ofstream ofile;
 int main(int argc, char* argv[])
 {
   char *outfilename;
-  double derivativex[1000];
+  double derivative;
   // Read in output file, abort if there are too few command-line arguments
   if( argc <= 3 ){
     std::cout << "Bad Usage: " << argv[0] <<

doc/Programs/LecturePrograms/programs/IntroProgramming/cpp/derivnofile.cpp

@@ -0,0 +1,27 @@
+#include <iostream>
+#include <cmath>
+#include <fstream>
+#include <iomanip>
+// Note: not using namespace for std
+
+// Begin of main program
+
+int main(int argc, char* argv[])
+{
+  double derivative;
+  // Read in output file, abort if there are too few command-line arguments
+  if( argc <= 2 ){
+    std::cout << "Bad Usage: " << argv[0] <<
+      " read number of integration points" << std::endl;
+    exit(1);
+  }
+  // extracting number of mesh points
+  int i = atoi(argv[1]);
+  double x = atof(argv[2]);  // reading x-value
+  double h = 1.0/((double) i); // setting up step size
+  double Derivative = (exp(x+h)-2.*exp(x)+exp(x-h))/(h*h);
+  double RelativeError = log10(fabs(Derivative-exp(x))/exp(x));
+  std::cout << std::setw(15) << std::setprecision(8) << "relative error=" << RelativeError << std::endl;
+  return 0;
+}
+