Skip to main content

Linear equations task

When we graduated that does not mean we should stop learning, this is what at least I believe. These days after graduation I worked on some projects, below is one of them:

This was a program I created after university to keep my skills, up-to-date.
As I am a passionate Mathematical, I created a program which allowed me to find out “determinant” of the 3x3 matrix coefficients and also find whether the matrix has any solution. In other word, I found out whether this matrix has any dependent or independent row. I used many Array, ArrayList, double and other primitive types to accomplish this program.

You can download the code here. Below is small part of code.

import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Scanner;

 * @author Mehdi Dana
 * @date 25/07/2012

public class MathDana {
  * @param args
  * @throws IOException 

 // round a double value
 public static double roundTwoDecimals(double d) {
  DecimalFormat twoDForm = new DecimalFormat("#.##");
  return Double.valueOf(twoDForm.format(d));
 // compare two arraylist, whether they are the same or not
 public static boolean compareArrayList(ArrayList< Double> arr1, ArrayList< Double> arr2){
  boolean ans = true;
  for(int i=0; i < arr1.size(); i++){
   double tem1 = roundTwoDecimals( arr1.get(i));
   double tem2 = roundTwoDecimals( arr2.get(i));
   if(tem1 != tem2){ 
    ans = false;
  return ans;

 // many methods here

 // main method
 public static void main(String[] args) throws IOException {
  try {
   // a lot code here
  }catch(Exception e){
   System.out.println("Your input is wrong");
   // e.printStackTrace(); // to track error if there is 



Popular posts from this blog

Why I don't have social media account?

Just to be clear, I do not have any social media accounts except LinkedIn. No Facebook, Twitter, Instagram etc. 
I used to use some of them but I dropped them all before 2013 and now I am clean for over 4 years. I kept LinkedIn because I use for business contact only.
Today, I came cross this video and found quite interesting as I agree with what he says. 

I always said, the social media website/app specially Facebook and Instagram are just a game. It's funny how some users write the fake status which they don't believe it themselves but other believe it and vice versa. 
If you are making money or adding value to your life by using these apps, then use it otherwise don't kid yourself and just get rid of them, simply. I know it's hard in the beginning but trust me, it worth it, you are not alone. 

I solved GCHQ puzzle and this is how I did it

Today, I was reading the BBC news and I stumbled upon this GCHQ puzzle:
Take the digits 1,2,3 up to 9 in numerical order and put either a plus sign or a minus sign or neither between the digits to make a sum that adds up to 100. For example, one way of achieving this is:
1 + 2 + 34 - 5 + 67 - 8 + 9 = 100, which uses six plusses and minuses. What is the fewest number of plusses and minuses you need to do this? I love to challenge myself with these kind of puzzles, so I solved this and here is how:
We have 9 numbers [1 to 9] and also we have three possible separators [+, - and nothing] which to fill the gap between numbers we have 8 combinations of separators, e.g. we have 1+2+3+4+5+6+7-89 which in this case we have six times plus, one minus and one time nothing. 
So, I need to find all possibilities of combination which total is: 6561

Then, hook the possible combinations into numbers and check the total, easy enough. Now print the solution.
I have written this algorithm in PHP but ea…

Laptop touchpad issue on Linux

I installed Linux (Ubuntu 16.4 LTS) on my new laptop, Fujitsu E series, all went well apart from touchpad which did not work at all. I spend few hours searching (AKA Googling) but could not find any hope. That was embarrassing for me who called himself professional Linux user but cannot fix touchpad issue, what about typical Linux user? there must be way, so I kept searching and reading until finally I found the fix and all is working now. Here is the fix if anyone has similar issue:

In cammed line, run:
sudo modprobe -r psmouse

It should work fine for now but only for current session, it may not work after restarting your laptop, so to add permanent fix, do:sudo vim /etc/modprobe.d/psmouse.conf

And add following, then save and exit.

options psmouse proto=imps

I used vim, you can use your favourite text editor such as gedit, vi etc. I hope this helps someone and save their time. Read more on modprobe.

Thank you for reading this, as always happy to hear from you.