function [phi,dphix,dphiy] = shape(nod,dmax,gs,v,dm)
% EFG shape function and it's derivative with linear base
L = length(v);    %高斯點(diǎn)的數(shù)目
won = ones(1,L);
nv = gs(1:2,v);   %影響接點(diǎn)的高四點(diǎn)坐標(biāo)
nvo=nv(1,:)+nv(2,:);
nv1=nv(1,:)-nv(2,:);
p = [won;nvo;nv1];
dif =nod*won-nv;     %節(jié)點(diǎn)到不同高四點(diǎn)的距離
t = dm(1:2,v)/dmax;

% WEIGHTS--W and dw are vectors
[w,dwdx,dwdy] = cubwgt(dif,t,v,dmax,dm);
B = p.*[w;w;w];
pp = zeros(3);
aa = zeros(3);
daax = zeros(3);
daay = zeros(3);
for i=1:L
pp = p(1:3,i)*p(1:3,i)';
aa = aa+w(1,i)*pp;
daax = daax+dwdx(1,i)*pp;
daay = daay+dwdy(1,i)*pp;
end

nod1=nod(1,1)+nod(2,1);
nod2=gpos(1,1)-gpos(2,1);
pg = [1 nod1 nod2];
Ainv = inv(aa);
phi = pg*Ainv*B;
dbx = p.*[dwdx;dwdx;dwdx];    %節(jié)點(diǎn)的形函數(shù)及其倒數(shù)
dby = p.*[dwdy;dwdy;dwdy];
dax = -Ainv *(daax*Ainv);
day = -Ainv *(daay*Ainv);
dphix = [0,1,1]*Ainv*B + pg*(dax*B + Ainv*dbx);
dphiy = [0,1,-1]*Ainv*B + pg*(day*B + Ainv*dby);