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diff --git a/tools/cosmo_calc/main.cc b/tools/cosmo_calc/main.cc
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+//
+// simple `cosmology calculator'
+// can calc commonly used cosmology distances:
+//      hubble distance
+//      comoving distance
+//      transverse comoving distance
+//      angular diameter distance
+//      luminoisity distance
+//      light-travel distance
+// in addition, this calculator also calc some other
+// useful infomation related with Chandra
+//
+// Junhua Gu
+//
+// Modified by: LIweitiaNux
+//
+// ChangeLogs:
+// v2.1, 2012/08/12, LIweitiaNux
+//   improve cmdline parameters
+// v2.2, 2013/02/09, LIweitiaNux
+//   add 'hubble_parameter E(z)'
+//   modify output format
+//
+
+
+#include "calc_distance.h"
+#include "ddivid.h"
+#include <cstdio>
+#include <cstdlib>
+#include <cmath>
+#include <iostream>
+
+using namespace std;
+
+// extern variables in `calc_distance.h'
+extern double cm;
+extern double s;
+extern double km;
+extern double Mpc;
+extern double kpc;
+extern double yr;
+extern double Gyr;
+extern double H0;           // units: [km/s/Mpc]
+extern double c;
+extern double omega_m;
+extern double omega_l;
+extern double omega_k;
+extern double arcsec2arc_ratio;
+
+// README, ABOUT
+static char DESC[] = "simple cosmology calculator";
+static char VER[]  = "v2.2, 2013-02-09";
+
+// setting parameters
+static double PI = 4*atan(1.0);
+// chandra related
+static double arcsec_per_pixel = 0.492;
+// above cosmology paramters can also be changed
+// through cmdline paramters
+
+// functions
+void usage(const char *name);
+
+//////////////////////////////////////////////
+// main part
+//////////////////////////////////////////////
+int main(int argc,char* argv[])
+{
+    double z;       // given redshift
+
+    // cmdline parameters
+    if (argc == 2) {
+        // get input redshift
+        z = atof(argv[1]);
+    }
+    else if (argc == 3) {
+        z = atof(argv[1]);
+        // use specified `H0'
+        H0 = atof(argv[2]);
+    }
+    else if (argc == 4) {
+        z = atof(argv[1]);
+        H0 = atof(argv[2]);
+        // get specified `Omega_M'
+        omega_m = atof(argv[3]);
+        omega_l = 1.0-omega_m;
+    }
+    else {
+        usage(argv[0]);
+        exit(-1);
+    }
+
+    // calc `Hubble parameter E(z)'
+    double E_z = E(z);
+    // calc `comoving distance'
+    double d_C = calc_comoving_distance(z);
+    // calc `angular diameter distance'
+    double d_A = calc_angdia_distance(z);
+    // calc `luminoisity distance'
+    double d_L = calc_luminosity_distance(z);
+
+    // output results
+    // parameters
+    printf("Parameters:\n");
+    printf("  z= %lf, H0= %lf, Omega_M= %lf, Omega_L= %lf\n",
+            z, H0, omega_m, omega_l);
+    printf("Distances:\n");
+    printf("  Comoving_distance: D_C(%lf)= %lg [cm], %lf [Mpc]\n",
+            z, d_C, d_C/Mpc);
+    printf("  Angular_diameter_distance: D_A(%lf)= %lg [cm], %lf [Mpc]\n",
+            z, d_A, d_A/Mpc);
+    printf("  Luminoisity_distance: D_L(%lf)= %lg [cm], %lf [Mpc]\n",
+            z, d_L, d_L/Mpc);
+    printf("Chandra_related:\n");
+    printf("  kpc/pixel (D_A): %lf\n",
+            (d_A / kpc * arcsec_per_pixel* arcsec2arc_ratio));
+    printf("  cm/pixel (D_A): %lg\n",
+            (d_A * arcsec_per_pixel* arcsec2arc_ratio));
+    printf("Other_data:\n");
+    printf("  Hubble_parameter: E(%lf)= %lf\n", z, E_z);
+    printf("  kpc/arcsec (D_A): %lf\n", (d_A / kpc * arcsec2arc_ratio));
+    printf("  norm (cooling_function): %lg\n",
+            (1e-14 / (4.0 * PI * pow(d_A*(1+z), 2))));
+
+    //cout<<ddivid(calc_distance,d,0,1,.0001)<<endl;
+
+    return 0;
+}
+
+// other auxiliary functions
+void usage(const char *name)
+{
+    cerr << "Usage: " << endl;
+    cerr << "    " << name << " z [H0] [Omega_M]" << endl;
+    // description
+    cout << endl << "About:" << endl;
+    cout << DESC << endl << VER << endl;
+}
+
+/* vim: set ts=8 sw=4 tw=0 fenc=utf-8 ft=cpp: */