Category: Other

AHP Alternative Evaluation – Weighted Sum or Weighted Product Model?

In AHP the preference Pi of alternative Ai is usually calculated using the weigthed sum model (WSM), i.e. calculation of global priorities for alternatives results from the additive aggregation of local preferences and criteria weights.

In my online software AHP-OS users can also select the weighted product model (WPM), where alternatives are aggregated using the product instead of the sum (Goepel 2018). We call this – in contrast to the classical (additive) AHP – multiplicative AHP or MAHP.

AHP-OS Group Result Menu: tick the wpm box and refresh to get the MAHP results.

Ishizaka, Balkenborg and Kaplan (2011) have shown that the additive AHP will overrate alternatives with extreme ratings and penalize balanced ones. Bafahm and Sun (2019) examine in their paper some abnormal results of AHP, contradictory to common expectations and basis decision-making logic in very simple cases. These conflicting results can be easily avoided using WPM.

Krejci and Stoklasa (2018) clearly show in their paper the superiority of using the weighted product model over the weighted sum model for the purpose of deriving global priorities of alternatives.

Aggregation of local priorities of alternatives into global priorities in AHP should not be done using the weighted sum model (WSM). Instead, the Weighted Product Method (WSM) should be used.

Literature

Bafahm A., Sun M. (2019). Some Conflicting Results in the Analytic Hierarchy Process, International Journal of Information Technology & Decision Making Volume 18, Issue 02 (March 2019) Pages:419–443 https://doi.org/10.1142/S0219622018500517

Goepel, K.D. (2018). Implementation of an Online Software Tool for the Analytic Hierarchy Process (AHP-OS). International Journal of the Analytic Hierarchy Process, Vol. 10 Issue 3 2018, pp 469-487 https://doi.org/10.13033/ijahp.v10i3.590

Ishizaka A., Balkenborg D., Kaplan T. (2011). Influence of aggregation and measurement scale on ranking a compromise alternative in AHP. Journal of the Operational Research Society (2011) 62: 700. https://doi.org/10.1057/jors.2010.23

Krejci J., Stoklasa J. (2018). Aggregation in the analytic hierarchy process: Why weighted geometric mean should be used instead of weighted arithmetic mean. Expert Systems with Applications Volume 114, 30 December 2018, Pages 97-106 https://doi.org/10.1016/j.eswa.2018.06.060

How to make your Synology Disk station (NAS) more secure?

Introduction

Recently I bought the network attached storage (NAS) DS1513+ from Synology and integrated it into my home network in order to have a central place to store and access my data. This NAS has several server functions, making it convenient to access data remotely, but also making it vulnerable to unauthorized intrusion. So the question arises, how to mitigate this risk without restricting the remote functionality of the NAS. There is a lot of information available in the web; yet for me it took some time to identify and understand the most important modifications and to implement them:

  1. VPN Virtual Private Network – to remotely access the local area home network
  2. SSH Secure Shell – for secure login as root user or admin to fully access the (embedded) operating system
  3. SSL/TLS – to secure traffic between website and browser (HTTPS)
  4. Enable 2-Step Verification for DSM web access
  5. Store all critical data (certificates and private keys) on an encrypted memory card

Continue reading How to make your Synology Disk station (NAS) more secure?

Fighting Spam

Operating your own website or blog, you will soon realize lots of comments with nonsense content and embedded links to obscure websites. These are comment spammers making your life difficult. Everyday you have to clean up or moderate all comments. In the past I used a wordpress plugin “spam free wordpress” to protect my blog, and for long time it was working fine without any problems. Writing a comment to my postings, you were asked to copy and paste a password from one to another field in the comment form. Suddenly it was not working any longer, and I found out that the developer changed his policy: I have to pay a license fee. Maybe I also should change my policy, and ask for a license fee to download my AHP excel template? So I was searching for a new free plugin. I installed SI Captcha Anti-Spam from Mike Challis, but still spam comments were coming through. So I enabled the honeypot spambot trap and it seems to work.

What is a honey pot spambot trap?

I learned some new things about spam, and also found an interesting project “Project Honey Pot” on the web. There you can find out more about harvesters, spammers, dictionary attackers and honey pots. You can participate in the project, install a honey pot or implement a quick link to fight spam. A honey pot is a – for humans invisible – link to a dynamic website providing “fake” e-mail addresses and forms for spam programs. If the form is submitted or an e-mail sent to one of addresses provided there, then you can be sure it is a spammer and record/block his IP address. Here an example of a quick link (opens in a separate window, don’t submit.) Usually this link is hidden -only visible for bots, spider programs etc.

Project Honey Pot also provides a useful service HTTP Blacklist to check IPs against a list of known harvesters, comment spammers, and other suspicious visitors to websites.

Now I can monitor  suspicious activities on my website: within only two days I could see more than 100 attacks!

Check your own IP address.

Video Editing Workflow – Canon XA-10

Source

Camera settings depend on the type of recorded video. The Canon XA-10 has only two full HD (1920×1080) recording modes: FXP and MXP. Based on these, most of my videos are recorded in FXP mode as it is a good trade-off between quality and file size.

Recording Modes of Canon XA-10

Edit and Archive

For video editing I use Adobe Premier Elements 10. Editing is done without changing codec (H264), resolution, interlacing, etc. As I have the PAL version of the XA-10, the Adobe project settings are AVCHD Full HD 1080i 25 under PAL. Once the video is edited, I  render the clip with the highest quality settings (2 Pass VBR, Render at max. depth, Macro block Adaptive Frame-Field Coding), and a maximum bitrate corresponding to the source (FXP: 17 Mbps) for archiving. In Adobe Premier Elements 10 and for XA-10 FXP mode the settings are:

Archive settings in Adobe Premier Elements 10 for XA-10 FXP mode

Target Media

Depending on the target media the clip to be published is adjusted in codec, resolution etc. I have predefined settings for:

  • Standard clips to be watched on a PC:
    MP4 – PAL DV Widescreen SD – HiQ (576p, VBR 3/6 MBps)
  • Tablet/phones:
    MP4 – PAL DV Widescreen SD – LoQ (576p, VBR 1.3/2.6 Mbps)
  • Youtube as basic HD clip:
    MP4 – HD 720p 25 (720p, VBR 2.5/5 Mbps)

Calculation of Video Bitrates in Excel

I use a simple excel template to calculate the bitrate for the target medium. As input you simply select:

  • Codec (H264, MPEG-2)
  • Standard (PAL, NTSC, FILM)
  • Definition (VCD, SD, HD 720, HD, full HD)
  • Channel (PC/Web, Disk/TV)
  • Action/Motion (low, normal, medium, high)

and as a result you get the recommended bitrate for rendering your video clip.

Comments and feedback are welcome!

Practical Experience with Canon XA-10

XA-10

Since a few months I use the Canon XA-10 camcorder to take the videos on this website, and when traveling. The video about the diversity index as business KPI, and the trip to the Philippines, visiting Bohol Island and Lake Taal, I shoot with the XA-10.

Overall I am quite o.k. with it, but a few details – like for example the tiny custom assignable buttons – are less satisfying. Now I am working on a review to share my experience. Stay tuned – and thanks for visiting.

Lake Taal -Philippines

Taal Lake is a freshwater lake in the province of Batangas, on the island of Luzon in the Philippines. The lake fills a large volcanic caldera formed by eruptions between 500,000 and 100,000 years ago. That crater lake is the world’s largest lake on an island in a lake on an island, and it in turn contains its own small island, Vulcan Point.

Enjoy Watching! If you like the video, leave a comment below.

Exploring Bohol, Philippines

ChocolateHillsBohol is a smaller island in the island grouping of the Visayas, Philippines, a nice place to spend your holidays. Beside the famous chocolate hills and the trasier conservation area, the video shows Bolo knife forging, the Loboc river cruise with a local rondalla music group, dancing the traditional Tinikling dance, dolphin watching with a visit to Balicasag and Virgin island, as well as the Baclayon church, Tagbilaran market and the Hinigdanan cave in Dauis. Enjoy watching!

if you like the video, leave a comment below.

Canon XA-10 Video Camera – Damage or normal?

Just now I realized a problem with my (still) quite new Cannon XA-10 camera. Obvious under low light conditions and white colored background the corners getting dark – vignetting; you see it clearly on the second picture. Of course – lens hood removed, it’s medium focal length …
Question: damage under warranty or normal?

Result from several visits and discussions with the Canon Service center in Singapore:

It is a limitation of the camera. (I would call it a design problem). Workaround: use manual focus & switch image stabilizer off (if possible use a tripod).

Making your wordpress blog more secure

You find the individual steps easily in a web search. Most critical is the change of SQL table prefixes. I did it manually using phpMyAdmin. When finished, no link was working any longer. Reason: permalinks were set to %postname%. After switching first to default and then back to %postname% everything was fine.

I also struggled with the password protection. Inportant: add the line ErrorDocument 401 default, otherwise you might always get the “page not found” message.

Steps to do:

  • Move config.php file one directory above wordpress installation directory
  • Remove admin user
    (create new user with full rights and delete old user)
  • Protect wp-admin and wp-includes directories
    (read for owner and group only = 751)
  • Hide wordpress version and login error messages
    Add in functions.php (in your ChildTheme directory):
    <?php remove_action(‘wp_head’, ‘wp_generator’);
    add_filter(‘login_errors’,create_function(‘$a’,”return null;”)); ?>
  • Delete readme.html file from web root directory
  • Password protect wp-admin directory (I used CPanel to create .htaccess).
    Modify .htaccess file in wp-admin – add:
    ErrorDocument 401 default
  • Modify .htaccess file in web root:
    <IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteBase /
    RewriteRule ^index\.php$ – [L]
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule . /index.php [L]
    </IfModule>
  • SQL: change prefixes of database tables from
    “wp_”  to “new_prefix_”

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