appinventor.pevest.com switch over to new web server will happen “soon”

As noted below, my current web host for appinventor.pevest.com web site has announced they are shutting down their business. Over the past week I have been working to move 5 web sites, software and databases from my old web host to a new web host. This does not directly affect Learn2c.org.

The new web host location for appinventor.pevest.com is up and running  but not yet accessible. I need to do testing before I redirect the pevest.com web URL to the new server – not yet sure what day this will be done.

When the pevest.com address is updated in the domain name servers, the switch over can take anywhere from a few hours up to 3 days.  As this is the 4th web site I have migrated (so far), this time I might have done it properly(!) and the switch over may be completely transparent – we hope!

There is no change – at this time – to the Learn2c.org web site. However, some files and program source code are stored behind the scenes at appinventor.pevest.com and might be briefly inaccessible during the process of bringing the new server and web site online.

Access to example source code files may be offline – December 2019

My Internet service provider informed its customers this morning that they will be discontinuing their web site hosting and email services in February of 2020. This means my appinventor.pevest.com web site, which has some of the example source code files, needs to be transferred to a new web service. During that transfer, access to some of the source files will be offline for a bit.

This will especially affect access to the sample source files featured in my App Inventor e-books.

I have 5 web sites that I need to move to a new server and the transfer process is somewhat complex. I do not yet know when this transfer will take place.

This post is an advance warning that this will be happening and hopefully file access will not be offline for long – when the transfer occurs. At this time, I have no date yet for when this process will be undertaken.

Source code downlinks fixed

Two readers alerted me to problems downloading the source code on the Downloads page on this web site, and the source code for my book on App Inventor graphics and animation.

A software update on the server appears to have changed how some default file directories were appended to filenames.

The problem appears to now be fixed. Thank you very much for letting me know of this problem  – let me know in comments if you encounter any further problems with the downloads.

Ed

Apologies for lack of updates

Sorry for the lack of updates and posts to this web site. I have had a lot going on – and right now, we are in process of moving across the state. Eventually things will be settled down. I completed several interesting App Inventor projects but have lacked time to get them posted here. Hang in there – I intend to be back!

Learn2c.org web site has a new, cleaner and simpler look

I have redesigned the Learn2c.org web site to feature this clean and simple look, with less clutter than I had on the prior design. Do not be alarmed – its the same web site as before!

The following is a cross-post from my older web site on App Inventor:

This web site – appinventor.pevest.com – is no longer the primary web site for our App Inventor tutorials. However, that web site will remain there indefinitely as many people link to it, including search engines and my own e-books 🙂

The new, short and easy to remember URL is Learn2C.org as in “Learn 2 Code”

Unfortunately, for reasons I will not get into, it is not possible to integrate the two web sites together. So appinventor.pevest.com will remain “as is”, and Learn2C.org is the  primary focus point.

I am looking into having Learn2C automatically cross post to the appinventor.pevest.com web site but that has not yet been implemented. But I’d like to do that for those that already follow the appinventor.pevest.com web site.

My apologies for not doing a lot of updates during 2018. I have already written some new code examples (Bluetooth LE anyone?) and am working on more in that area. These tutorials will appear once I have completed the entire series of example programs. There are also other items in the works that I cannot talk about yet.

Google will be discontinuing Google Fusion Tables at end of 2019

Google created a cloud-based data base system called Fusion Tables. Later, support for Fusion Tables was added to App Inventor.

Google has sent out an email advising Fusion Tables users that they will be discontinuing Fusion Tables – literally, the database service will go away on 3 December 2019.

If you have used Fusion Tables, you will need to update the code to use a new data base system. You might consider third-party App Inventor-based development systems such as Appy Builder.

Hello,

Google Fusion Tables was launched almost nine years ago as a research project in Google Labs, later evolving into an experimental product. For a long time, it was one of the few free tools for easily visualizing large datasets, especially on a map. Since then, Google has developed several alternatives, providing deeper experiences in more specialized domains.

In order to continue focusing our efforts in these areas, we will be retiring Fusion Tables. We plan to turn down Fusion Tables and the Fusion Tables API on December 3, 2019. Embedded Fusion Tables visualizations — maps, charts, tables and cards — will also stop working that day. Maps using the Fusion Tables Layer in the Maps JavaScript API v3.37 will start to see errors in August 2019.

Here are some next steps to consider:

Learn about alternative toolsSeveral new Google tools have been developed over the years, and we encourage you to visit the Help Center to learn which ones fit your use-case.

Teams at Google have developed internal tools that can create powerful map visualizations. We are working to make some of these tools publicly available and will have more to share in the coming months—sign up to stay in touch.

Download your dataFilter by “type:table” to pull up a list of your tables in Google Drive. Download data from an individual table by following these instructions. If you have a lot of tables, we will make it easy to download all your data in one step via Google Takeoutstarting in March 2019.

Thank you for supporting Fusion Tables over the years. If you have feedback, visit the Fusion Tables Help Forum.

Sincerely,
The Google Fusion Tables Team

Calculating a square root value

A reader asked a question about how square roots can be calculated, referring to an example in my Volume 1 Introduction to App Inventor e-book. He was confused by the explanation of how it works – so I have written an expanded explanation of the method for calculating a square root of a number.

You could use the built in Math function to find the square root of a number – and generally that is what you should do. But if you would like to learn a method of calculating the square root of a number – then read on!

2,000 years ago, Greek mathematicians identified a method of finding approximate square roots. The method makes an initial guess of a square root (which is often not even close to the right value) and then repeats a sequence of dividing and averaging which gradually refines the initial guess into an accurate square root.  To find the square root of some number n, we set our initial guess to n (which we know is not correct), and then calculate an average of our guess with n divided by our guess.

To find the square root of 30, we initially guess the square root is 30 (which we know is wrong). We then take 30 and divide it by our guess, which in this case is 30. This gives us a value of 1. The average of our original number 30 and our divided value is 15.5. We select 15.5 as our new guess.

This little spreadsheet may help understand how the square root concept works.

To find the square root of 30, we initially guess the square root is 30 (which we know is wrong). We then take 30 and divide it by our initial guess, which is 30. This gives  a value of 1. The average of our original number 30 and 1 is 15.5. We select 15.5 as our new guess on the next row down in the Guess column.

Then we repeat this and take 30 divided by our new guess of 15.5. This gives us 1.93548. We average our 15.5 guess with our new value of 1.9458 giving us 8.717, which becomes our new guess on the next row down.

We repeat again using 8.717 as our new guess and divide 30 by 8.717, giving us 3.44. We average the 8.717 with 3.44 giving us 6.0795, use that as our next guess.

When do we stop this repeating cycle? We could repeat this a set number of times, say six, and then stop. But a better solution is to specify how many digits of accuracy we would like to have in our answer.

Let’s say that 5.4 is accurate enough for our purposes. We could stop as soon as our new guess is within 0.1 of our prior guess. In our spreadsheet above, our generated guesses are:

  • 15.5
  • 8.717742
  • 6.0795
  • 5.507058
  • 5.477306
  • 5.477226

As you can see, the correct answer has converged to 5.477 rather quickly. If we wanted an accuracy of just 1 digit to the right of the decimal point, we can stop once the difference between the current and previous guess is 0.1

The first digits of the last two guesses are the same 5.4 so we could stop with an accuracy of .1. In this particular calculation, we see that we are accurate to the thousandth’s place 5.477 as these values are no longer changing.

We stop the cycle when the difference between guesses becomes very small.

With our definition of small to 0.1, we stop at 5.4. If we set our definition of small difference to 0.001, then we stop at 5.477.

Here is some sample App Inventor code that calculates the square root. It fetches the number for which we find the square root from a user interface Text Box named txtDataEntry. We set NewValue (our initial guess) to this value. Then the code uses a while test loop to repeatedly do the calculation while the difference between our new guess and our previous guess is greater than 0.1 (you can change this to smaller values for greater accuracy).

This square root calculation repeats as long as the difference between our NewValue and OldValue are large.

As long as the difference remains large, the while test condition is “true”, and the code inside the while block continues to execute. However, once the difference becomes small, the test condition evaluates to “false” and the the execution of the “do” section stops. We have found our approximate square root.

The most popular programming languages

There are many surveys of programming language popularity. Many of the popular surveys have problems with the survey methodology such that they likely produce erroneous estimates of programming language popularity. For example, one survey looks at how many times each programming language is looked up on Internet search systems.

The chart, below, comes from GitHub and bases popularity on the number of “pull requests” that are made to the GitHub software repository. Using this method, JavaScript is the most popular programming language, followed by Python, Java, Ruby and PHP.

Python has become a standard for use by non-computer science students. Whether your college studies be in mechanical engineering or geology, there is a good chance you will learn Python for data analysis projects.

Java is now an old programming language, but still used especially for Android programming. It’s popularity for desktop applications is starting to diminish.

Ruby become popular about ten years ago. Ruby is based on a concept of “frameworks” that provide pre-made program skeletons which you adapt to make your own application. Ruby is very popular for quickly creating web-based applications.

PHP pre-dates Ruby – PHP is a script language that runs on the server side of a web application. PHP is very easy to learn and couples easily with MySQL databases, making the combination a great solution for web-based, database-backed applications.

Finally we get to the “C” derived languages including C, C++ and Microsoft’s cousin C# (a very powerful language with great development tools.). C dates back to about 1970 or so.

C++ was developed in the 1980s and added object oriented programming to C and has since expanded in many ways. C and C++ are commonly “compiled” into machine instructions for each CPU and are used for high performance applications, including operating systems, video games and media applications.

C# has features resembling Java and C++ – but in a more modern design. In some ways, C# is where some wish C++ had gone 🙂

Capture

Interested in JavaScript programming?

A follow up to my earlier post asking about interest in other programming languages.

How about JavaScript? JavaScript is widely used in web development, can be programmed with a text editor and tested with a browser – you do not need to download and install development software.

Another plus, if you do choose to download an Integrated Development Environment, you can then package your JavaScript apps within PhoneGap and run them on Android and iOS devices. Thus, JavaScript is another way to write apps for Android (and iOS) that goes beyond App Inventor.

My thinking is this topic could be of interest to those wishing to leverage their App Inventor programming on to other types of programming. The idea would be to create tutorials that leverage what you know about App Inventor (hopefully!) and translate that into JavaScript.

For now, this is just an idea. Looking for feedback!

The quick and easy way to write Android Apps

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