function [x,y]=poissong(bs,s)%POISSONG	Gives geometry data for the poissong PDE model.%%   NE=POISSONG gives the number of boundary segments%%   D=POISSONG(BS) gives a matrix with one column for each boundary segment%   specified in BS.%   Row 1 contains the start parameter value.%   Row 2 contains the end parameter value.%   Row 3 contains the number of the left-hand regions.%   Row 4 contains the number of the right-hand regions.%%   [X,Y]=POISSONG(BS,S) gives coordinates of boundary points. BS specifies the%   boundary segments and S the corresponding parameter values. BS may be%   a scalar.nbs=4;if nargin==0,  x=nbs; % number of boundary segments  returnendd=[  0 0 0 0 % start parameter value  1 1 1 1 % end parameter value  0 0 0 0 % left hand region  1 1 1 1 % right hand region];bs1=bs(:)';if find(bs1<1 | bs1>nbs),  error('Non-existent boundary segment number')endif nargin==1,  x=d(:,bs1);  returnendx=zeros(size(s));y=zeros(size(s));[m,n]=size(bs);if m==1 & n==1,  bs=bs*ones(size(s)); % expand bselseif m~=size(s,1) | n~=size(s,2),  error('bs must be scalar or of same size as s');endif ~isempty(s),% boundary segment 1ii=find(bs==1);if length(ii)x(ii)=(5-(-5))*(s(ii)-d(1,1))/(d(2,1)-d(1,1))+(-5);y(ii)=(5-(5))*(s(ii)-d(1,1))/(d(2,1)-d(1,1))+(5);end% boundary segment 2ii=find(bs==2);if length(ii)x(ii)=(5-(5))*(s(ii)-d(1,2))/(d(2,2)-d(1,2))+(5);y(ii)=(-5-(5))*(s(ii)-d(1,2))/(d(2,2)-d(1,2))+(5);end% boundary segment 3ii=find(bs==3);if length(ii)x(ii)=(-5-(5))*(s(ii)-d(1,3))/(d(2,3)-d(1,3))+(5);y(ii)=(-5-(-5))*(s(ii)-d(1,3))/(d(2,3)-d(1,3))+(-5);end% boundary segment 4ii=find(bs==4);if length(ii)x(ii)=(-5-(-5))*(s(ii)-d(1,4))/(d(2,4)-d(1,4))+(-5);y(ii)=(5-(-5))*(s(ii)-d(1,4))/(d(2,4)-d(1,4))+(-5);endend