26 lines
516 B
Mathematica
26 lines
516 B
Mathematica
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function [A,xy] = gridt(k)
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% GRIDT : Generate triangular mesh.
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%
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% [A,xy] = GRIDT(k) returns a k*(k+1)/2-square symmetric positive
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% definite matrix A with the structure of an equilateral triangular
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% mesh with side k, and an array xy of coordinates of the mesh points.
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% Start with a square 7-point grid.
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[A,xy] = grid7(k);
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% Mask off one triangle of it.
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xy = xy-1;
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f = find(xy(:,1)+xy(:,2)<k);
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A = A(f,f);
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xy = xy(f,:);
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% Make the other triangle equilateral.
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T = [ 1 0 ; 1/2 2/sqrt(5)];
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xy = xy*T;
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end
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