added solution to 5.1 to 5.4

exercises/ex05/solutions/conv1.mod

+reset;
+
+var x >= -2.5;
+var y >= -2.5;
+minimize obj: x^2 - y^2;
+s.t. c: x^2 + y^2 <= 1;
+
+option solver cplex;
+solve;

exercises/ex05/solutions/conv2.mod

+reset;
+
+var x >= -2.5;
+var y >= -2.5;
+minimize obj: x^2 - y^2;
+s.t. c: x^2 + y^2 <= 1;
+
+option solver cplex;
+option cplex_options "reqconvex=2";
+solve;
+display obj, x, y;

exercises/ex05/solutions/conv3.mod

+reset;
+
+var x >= -2.5;
+var y >= -2.5;
+minimize obj: x^2 - y^2;
+s.t. c: x + y <= 1;
+
+option solver cplex;
+option cplex_options "reqconvex=2";
+solve;
+display obj, x, y;

exercises/ex05/solutions/conv4.mod

+reset;
+
+var x >= -2.5;
+var y >= -2.5;
+minimize obj: x^2 - y^2;
+s.t. c: x + y <= 1;
+
+option solver cplex;
+option cplex_options "reqconvex=3";
+solve;
+
+display obj, x, y;

exercises/ex05/solutions/conv5.mod

+reset;
+
+var x >= -2.5;
+var y >= -2.5;
+minimize obj: x^2 - y^2;
+s.t. c: x + y <= 1;
+
+option solver gurobi;
+solve;

exercises/ex05/solutions/conv6.mod

+reset;
+
+var x >= -2.5;
+var y >= -2.5;
+minimize obj: x^2 - y^2;
+s.t. c: x + y <= 1;
+
+option solver xpress;
+solve;
+display _var;

exercises/ex05/solutions/conv7.mod

+reset;
+
+var x >= -2.5;
+var y >= -2.5;
+minimize obj: x^2 - y^2;
+s.t. c: x + y <= 1;
+
+option solver scip;
+solve;
+display obj,x,y;

exercises/ex05/solutions/conv8.mod

+reset;
+
+var x >= -2.5 := 0.0;
+var y >= -2.5 := -1.0;
+minimize obj: x^2 - y^2;
+s.t. c: x^2 + y^2 <= 1;
+
+option solver scip;
+solve;
+display obj, x, y;

exercises/ex05/solutions/conv9.mod

+reset;
+
+var x >= -2.5 := 0;
+var y >= -2.5 := -1;;
+minimize obj: x^2 - y^2;
+s.t. c1: x^2 + y^2 >= 1;
+s.t. c2: x^2 + y^2 <= 3;
+
+option solver scip;
+solve;
+display obj, x, y;