# RPN Calculator

Reverse Polish Notation is a method of notation of mathematical expressions that allows simple calculations to be performed without the need of using brackets – thanks to the use of a stack. This method has been popularized by Hewlett Packard, which has been successfully using it in its calculators for many years.

The Artinu application is a simple RPN calculator, written in JavaScript, available online:

# COVID-19 Death Rate

Update:

We present death rate versus time chart for selected countries: Brazil, Germany, Italy, US, Poland, Sweden, Switzerland. Death rate is calculated as follows:
$$d = \frac{N_\mathrm{deaths}}{N_{\mathrm{infected}}} \cdot 100,$$
where $$N_\mathrm{deaths}$$ is number of deaths caused by COVID-19 infection since the beginning of epidemic, $$N_{\mathrm{infected}}$$ is a total number of infected people. For each country, the plot starts at the first date where there are at least 100 infected cases, which is common practice.

# The limits of central limit theorem – part 2

In the previous part we made look through the distribution of sample means for three distributions: Uniform, Cauchy, and Petersburg distribution. The Cauchy and Petersburg distributions do not fulfill the Central Limit Theorem since they have infinite variance (and infinite expected value in “Petersburg” case). Now we will have a look at the numerical results for standard deviation of sample means. As in previous part, we use Uniform distribution only as a reference since it fulfills CLT and we use the same pseud-random number generator (Mersenne-Twister).