Seasonality Index of extreme events

% This function can be use to calculate seasonal distribution of any exteme
% events in hydrology namely, low flows or maximum flow. It relies on two
% parameter, namely :
% r: the length of the mean vector is a measure of the variability of low flow days
% theta: the directional angle of the mean vector.
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% Code is written by Pankaj Dey, PhD student at Department of Civil
% Engineeing, Indian Institute of Science, Bangalore.
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% Input: date: it is an array which compose of the dates when the extermes
% are observed in a particular year. The structure of date is as follows:
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%For example: Col.1 Col.2 Col.3
% Year Month Day
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% date= 1904 3 1
% 1905 3 1
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% Output: results: a matrix whose
% First row element denotes the length of the
% mean vector
% Second row element denotes the directional
% angle of the mean vector
% Third row element denotes the mean day of
% occurence of extreme.
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% Additionally a polar plot will pop up ehich will graphically display the
% position of the mean vector in polar cordiantes.
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% Note: a function name 'date2julian' is used in this function.
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% References: Laaha, G. and Blöschl, G., 2006. Seasonality indices for regionalizing low flows. Hydrological Processes, 20(18), pp.3851-3878.
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