boundary_conditions.m

%---------------------------------------------------------------------------------------
% defines new extrema points to extend the interpolations at the edges of the
% signal (mainly mirror symmetry)
% Written by Gabriel Rilling
function [tmin,tmax,zmin,zmax] = boundary_conditions(indmin,indmax,t,x,z,nbsym)

lx = length(x);

if (length(indmin) + length(indmax) < 3)
error('not enough extrema')
end

    % boundary conditions for interpolations :

if indmax(1) < indmin(1)
    if x(1) > x(indmin(1))
lmax = fliplr(indmax(2:min(end,nbsym+1)));
lmin = fliplr(indmin(1:min(end,nbsym)));
lsym = indmax(1);
else
lmax = fliplr(indmax(1:min(end,nbsym)));
lmin = [fliplr(indmin(1:min(end,nbsym-1))),1];
lsym = 1;
end
else

if x(1) < x(indmax(1))
lmax = fliplr(indmax(1:min(end,nbsym)));
lmin = fliplr(indmin(2:min(end,nbsym+1)));
lsym = indmin(1);
else
lmax = [fliplr(indmax(1:min(end,nbsym-1))),1];
lmin = fliplr(indmin(1:min(end,nbsym)));
lsym = 1;
end
end
   
if indmax(end) < indmin(end)
if x(end) < x(indmax(end))
rmax = fliplr(indmax(max(end-nbsym+1,1):end));
rmin = fliplr(indmin(max(end-nbsym,1):end-1));
rsym = indmin(end);
else
rmax = [lx,fliplr(indmax(max(end-nbsym+2,1):end))];
rmin = fliplr(indmin(max(end-nbsym+1,1):end));
rsym = lx;
end
else
if x(end) > x(indmin(end))
rmax = fliplr(indmax(max(end-nbsym,1):end-1));
rmin = fliplr(indmin(max(end-nbsym+1,1):end));
rsym = indmax(end);
else
rmax = fliplr(indmax(max(end-nbsym+1,1):end));
rmin = [lx,fliplr(indmin(max(end-nbsym+2,1):end))];
rsym = lx;
end
end
   
tlmin = 2*t(lsym)-t(lmin);
tlmax = 2*t(lsym)-t(lmax);
trmin = 2*t(rsym)-t(rmin);
trmax = 2*t(rsym)-t(rmax);
   
% in case symmetrized parts do not extend enough
if tlmin(1) > t(1) || tlmax(1) > t(1)
if lsym == indmax(1)
lmax = fliplr(indmax(1:min(end,nbsym)));
else
lmin = fliplr(indmin(1:min(end,nbsym)));
end
if lsym == 1
error('bug')
end
lsym = 1;
tlmin = 2*t(lsym)-t(lmin);
tlmax = 2*t(lsym)-t(lmax);
end  
   
if trmin(end) < t(lx) || trmax(end) < t(lx)
if rsym == indmax(end)
rmax = fliplr(indmax(max(end-nbsym+1,1):end));
else
rmin = fliplr(indmin(max(end-nbsym+1,1):end));
end
if rsym == lx
error('bug')
end
rsym = lx;
trmin = 2*t(rsym)-t(rmin);
trmax = 2*t(rsym)-t(rmax);
end
         
zlmax =z(lmax);
zlmin =z(lmin);
zrmax =z(rmax);
zrmin =z(rmin);
    
tmin = [tlmin t(indmin) trmin];
tmax = [tlmax t(indmax) trmax];
zmin = [zlmin z(indmin) zrmin];
zmax = [zlmax z(indmax) zrmax];
end

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