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%  1 Step of the elliptic solver (SOR) used in oct_get_psi.m
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%  penven 21-10-2001
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% Get the rhigh hand side terms of the equations
%
rhs(2:end-1,2:end-1)=...
a2(2:end-1,2:end-1).*psi(2:end-1,3:end)+...
a3(2:end-1,2:end-1).*psi(2:end-1,1:end-2)+...
a4(2:end-1,2:end-1).*psi(3:end,2:end-1)+...
a5(2:end-1,2:end-1).*psi(1:end-2,2:end-1)+...
b1(2:end-1,2:end-1).*psi(2:end-1,2:end-1)+...
b2(2:end-1,2:end-1).*xi(2:end-1,2:end-1);
%
% Step PSI
%
psi(ijeven==parity)=psi(ijeven==parity)-...
                    W.*rhs(ijeven==parity)./...
                    b1(ijeven==parity);
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% Advance the surrelaxation parameter
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W=1/(1-J2*W/4);
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% Apply the mask (not the islands bcpsi~=0)
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psi(isfinite(bc))=bc(isfinite(bc));
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%
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return
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%
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