27 lines
814 B
Mathematica
27 lines
814 B
Mathematica
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function Model = find_internal(pos,x)
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n = length(x);
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% Binary to model if element is non-zero
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dp = binvar(1,n); % Positve
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dn = binvar(1,n); % Negative
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d = binvar(1,n);
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% Binary to model if element is first non-zero
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e = binvar(1,n);
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[M,m] = derivebounds(x);
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M = max(max(abs(M),max(abs(m))));
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% Activate d iff value is sufficiently non-zero
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Model = [x <= 0.00001 + M*dp, x >= -0.00001 - M*dn, -M*d <= x <= M*d,
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x >= 0.00001-M*(1-dp), x <= -0.00001 + M*(1-dn)];
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% e(i) should be 1 if d(i) is the first 1
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Model = [Model, d == dn + dp, e(1) == d(1), sum(e)==1];
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for i = 2:n
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% No non-zeros so far so e must be 0
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Model = [Model, e(i) <= sum(d(1:i))];
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% Has to be activated if first 1
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Model = [Model, e(i) >= d(i)-sum(d(1:i-1))];
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end
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Model = [Model, integer(pos), pos == sum(e.*(1:n))];
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