Engineering and technology notes

GeoGebra

Jovan Stosic October 6, 2019

GeoGebra is an interactive geometry, algebra, statistics and calculus application, intended for learning and teaching mathematics and science from primary school to university level. GeoGebra is available on multiple platforms with its desktop applications for Windows, macOS and Linux, with its tablet apps for Android, iPad and Windows, and with its web application based on HTML5 technology.

Its creator, Markus Hohenwarter,[1] started the project in 2001 (as part of his master’s thesis) at the University of Salzburg, continuing it at Florida Atlantic University (2006–2008), Florida State University (2008–2009), and now at the University of Linz together with the help of open-source developers and translators all over the world.

After a successful Kickstarter campaign, GeoGebra expanded their offerings to include an iPad, an Android and a Windows Store app version.[2]

In 2013, Bernard Parisse’s Giac was integrated into GeoGebra’s CAS view.[3]

GeoGebra includes both commercial and not-for-profit entities that work together from the head office in Linz, Austria, to expand the software and cloud services available to its user community.

Source: GeoGebra – Wikipedia

Kotlin vs Java: Which programming language to choose for your Android application

Jovan Stosic October 1, 2019

In the Android development community, usage for Kotlin continues to grow, especially since its introduction as a preferred language by Google in 2017. So, which language should you choose for developing your app for Android? This article goes over some of the benefits that developing in Kotlin has over Java.

https://jaxenter.com/kotlin-java-android-162038.html

Daniel Defoe

Jovan Stosic September 29, 2019

Daniel Defoe (/dɪˈfoʊ/; c. 1660 – 24 April 1731), born Daniel Foe, was an English trader, writer, journalist, pamphleteer and spy. He is most famous for his novel Robinson Crusoe, which is second only to the Bible in its number of translations. He has been seen as one of the earliest proponents of the English novel, and helped to popularise the form in Britain with others such as Aphra Behn and Samuel Richardson.Defoe wrote many political tracts and often was in trouble with the authorities, including a spell in prison. Intellectuals and political leaders paid attention to his fresh ideas and sometimes consulted with him.

Defoe was a prolific and versatile writer, producing more than three hundred works—books, pamphlets, and journals—on diverse topics, including politics, crime, religion, marriage, psychology, and the supernatural. He was also a pioneer of business journalism and economic journalism.

https://en.wikipedia.org/wiki/Daniel_Defoe

Top 20 Best Computer Algebra Systems for Linux in 2019

Jovan Stosic September 19, 2019

The main functionalities of a CAS are to perform numerical computations, symbolic computations, data analysis, and data visualization. Due to its widespread domain, various computer algebra systems for Linux exist, dealing with different types of applications. Our editors have outlined 20 best computer algebra systems that can be used by mathematicians, data science professionals, or higher-studies purposes.

Source: Top 20 Best Computer Algebra Systems for Linux in 2019

About FFT of sine wave – MATLAB Answers

Jovan Stosic September 19, 2019
i just do the FFt of a sine wave :
t=0:0.01:1; A=sin(2*pi*10*t);
The FFt is:
U=fft(A,200); plot(abs(U));
Question is why the amplitude of fft is 50 and not 1 (convolution betwen sine wave spectrum and rect spectrum 1*1*sincf
——————–
It is because you have 101 points in your signal. Therefore the magnitude of the DFT at the frequency is going to be approximately N/2 where N is the number of points. If your sine wave had an amplitude other than 1, you would see NA/2
To make this exact, let’s create your sine wave with 100 points so that the frequency of 10-Hz falls directly in a DFT bin
t = 0:0.01:1-0.01;
x = cos(2*pi*10*t);
xdft = fft(x);
plot(abs(xdft))
Now you see the magnitude at -100 and 100 Hz is 100/2=50
Change the amplitude of the sine wave:
x = 3*cos(2*pi*10*t);
xdft = fft(x);
plot(abs(xdft))
Now the magnitude at -100 and 100 Hz is (3N)/2=150
This dependence on N comes from the fact that the DFT sums all the element-by-element products of your signal and complex exponentials with frequencies of (kFs)/N where Fs is the sampling frequency and N is the length of the signal and k=0,1,2,3, N-1
When your signal matches the frequency of one of those complex exponentials exactly, as is the case above, you get the coherent sum that results in N times the amplitude. Since your input is a cosine remember that results in TWO complex exponentials each with amplitude 1/2 the amplitude of the cosine.

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Source: About FFT of sine wave – MATLAB Answers – MATLAB Central