conv5.mod: Gurobi complains that quadratic objective is not positive definite.
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5.3
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Xpress
conv6.mod: Xpress complains that quadratic objective is not conves.
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5.4
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SCIP
conv7.mod: optimal solution found (0,-2.5).
Original problem with (convex) quadratic constraints.
conv8.mod: optimal solution found, (0,1).
There is another solution in (0,-1) (the problem is non-convex).
Problem with non-convex feasible set.
conv9.mod: optimal solution found (0,1.73).
There is another solution in (0,-1.73) (the problem is non-convex).
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5.5
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See svm.mod.
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5.6
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See mdr.m.
You need to double the number of variables, since now for each x_i there are x_i^+ (that is equal to x_i if x_i>0 and equal to 0 otherwise), and x_i^- (that is equalt to 0 if x_i>0 and equal to -x_i otherwise).