sin_sym.m

function Y = sin_sym(X)
%function Y = sin_sym(X)
%
% sine function guaranteeing exact floating-point symmetry
% i.e. sin(x) = sin(x+2*pi) = - sin(-x)
% i.e. usually we get 
%
%  sin(0.1) + sin(0.1+pi) = 4.1633e-17
%  sin_sym(0.1) + sin_sym(0.1+pi) = 4.1633e-17
%  
% Bernard Haasdonk 5.6.2008

% averaging over 4 periods:

%generate large lookuptable

resolution = 1000;
step = pi/resolution;
xvals = 0:step:(pi-1e-10);
if length(xvals)~=resolution;
  error('check length of table!!');
end;
sin_tab = sin(xvals);
sin_tab = [sin_tab, 0];
sin_tab(1:end) = 0.5*(sin_tab(1:end)+ sin_tab(end:-1:1));

% map X to interval 

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