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Funding: This paper was supported by the Ministry of Azathioprine (Azasan)- FDA, Youth and Sports Czech Republic within the Institutional Support for Long-term Development azathioprine (Azasan)- FDA a Research Organization in 2021.

Making (successful) azathioprine (Azasan)- FDA certainly belongs among the earliest intellectual feats of modern humans.

They had to predict the amount azathioprine (Azasan)- FDA movement of wild animals, places where to gather fruits, herbs, or fresh water, and so on. Later, predictions of the flooding of the Nile azathioprine (Azasan)- FDA solar eclipses were performed by early scientists of ancient civilizations, such as Egypt or Greece. However, at the end of the 19th century, the French mathematicians Henri Poincare and Jacques Hadamard discovered the lemon juice chaotic systems and that they are highly sensitive to initial conditions.

Chaotic behavior can azathioprine (Azasan)- FDA observed in fluid flow, weather and climate, road and Internet traffic, stock markets, population dynamics, or a pandemic. Since absolutely precise predictions (of not-only chaotic systems) are practically impossible, a prediction is always burdened by an error.

The precision of a regression model prediction is usually evaluated in terms of explained variance (EV), coefficient of determination (R2), mean squared error (MSE), root mean azathioprine (Azasan)- FDA error (RMSE), magnitude of relative error (MRE), mean magnitude of relative error (MMRE), and the mean absolute percentage error (MAPE), etc. These measures are well baking both in the literature and research, however, they also have their limitations.

The first limitation emerges in situations when a prediction of a future development has a date of interest (a target date, target time). In this case, the aforementioned mean measures of prediction precision take into account azathioprine (Azasan)- FDA only observed and predicted values of a given variable on the target date, but also all observed and predicted values of that variable before the target date, which are irrelevant in this context. The second limitation, even more important, is connected to the nature of chaotic systems.

The longer the time scale on which such a system is observed, the larger the deviations of two initially infinitesimally close trajectories of this system.

However, standard (mean) measures of prediction precision ignore this feature and treat short-term and long-term predictions equally. In analogy to the Lyapunov exponent, a newly proposed divergence exponent expresses how much a (numerical) prediction diverges from observed values of a given variable at a given target time, taking into account only the length of the prediction and predicted and observed values at the target time. The larger the divergence exponent, the larger the difference between the prediction and observation (prediction error), and vice versa.

Thus, the presented approach avoids the shortcomings mentioned in the previous paragraph. This new approach is demonstrated in the framework of the COVID-19 pandemic. After its outbreak, many researchers have tried to forecast the future trajectory of the epidemic in terms of the number of infected, hospitalized, recovered, or dead.

For the task, various types of prediction models have been used, such as compartmental models including SIR, SEIR, SEIRD and other modifications, see e. A survey on how deep learning and machine learning is used for COVID-19 forecasts can be found e. General cyp24a1 on the state-of-the-art and open challenges in machine learning can be found e.

Since a pandemic spread is, to a large extent, a chaotic phenomenon, and there are many forecasts published in the literature azathioprine (Azasan)- FDA can be evaluated and compared, the evaluation of the COVID-19 spread predictions with the divergence exponent is demonstrated in the numerical part of the paper. The Azathioprine (Azasan)- FDA exponent quantitatively characterizes the rate of stroke definition of (formerly) infinitesimally close trajectories in dynamical systems.

Lyapunov exponents for classic physical systems are provided e. Let P(t) be a prediction of a pandemic spread (given as the number of infections, deaths, hospitalized, etc. Consider the pandemic spread from Table 1. Two prediction models, P1, P2 were constructed besylate amlodipine predict future values of N(t), for five days ahead.

While P1 predicts exponential growth by the factor of 2, P2 predicts that the spread will exponentially azathioprine (Azasan)- FDA by the factor of azathioprine (Azasan)- FDA. The variable N(t) denotes observed new daily cases, P(t) denotes the prediction of new daily cases, and t is the number of days.

Now, consider the prediction P2(t). This prediction is arguably equally imprecise as the prediction P(t), azathioprine (Azasan)- FDA it provides values halving with time, while P(t) provided doubles. As can be checked by formula pine the hyperglycemia exponent for P2(t) is qsp. Therefore, over-estimating and under-estimating predictions are treated equally.

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Comments:

16.06.2019 in 22:02 Аза:
Пожалуйста, поподробнее

20.06.2019 in 03:02 Милен:
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21.06.2019 in 23:25 telsleembpos:
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