# How to generate Q4 element mesh in selected area?

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waqas on 8 Sep 2021
Answered: darova on 8 Sep 2021
Hi,
I have a region ( variable 'nmask' in the .MAT file) on which I want to generate a Q4 mesh. In my current implementation, the nodes are not falling perfectly on the boundary of the region. Figure below should explain it further where red markers show the location of the nodes. Following code was used to generate these:
tx = mfc:subset:mlc;
ty = mfr:subset:mlr;
[TX,TY] = meshgrid(tx,ty);
nodeDetails = [(1:size(TX,1)*size(TX,2))', TY(:),TX(:)];
%Connectivity Matrix
c = 0;
conect = zeros((size(TX,1)-1)*(size(TX,2)-1),4);
for j = 0:(size(TX,2)-2)
for i = 1: size(TX,1)-1
c = c + 1;
ii = j*(size(TX,1)) + i;
conect(c,:) = [ii, ii + 1, ii + size(TX,1) + 1, ii + size(TX,1)];
end
end
I am only interested in the white region. How can I also discard the other points? darova on 8 Sep 2021
x = [-10:-8 -7:7 8:10];
y = [-8:-6 -5:5 6:8];
[X,Y] = meshgrid(x,y);
i1 = -8<X & X<8 & -6<Y & Y<6; % inside region
i2 = X<0 & abs(Y)<2; % small hole right side
ind = i1 | i2;
Z = X*0;
Z(ind) = nan; % remove inside part
plot(X(:),Y(:),'.r') % whole mesh
surface(X,Y,Z)
view(45,45) 