added solution to 2.1 2.2

exercises/ex02/solutions/sing.mod

+reset;
+
+var x1 := 0;
+var x2 := 1;
+
+s.t. eq1: x1 + x1*x2 + x2^2 = 0;
+s.t. eq2: x1^2 - 2*x1 + x2^2 = 0;
+
+#option solver snopt;
+#option solver minos;
+#option solver ipopt;
+option solver knitro;
+
+#option minos_options "outlev=2";
+option knitro_options "outlev=2 feastol=0";
+
+solve;
+
+display x1, x2;

exercises/ex02/solutions/trig.mod

+reset;
+
+param n := 10;
+
+var x{i in 1..n} := 1/n;
+#var x{i in 1..n} := 1/n*(-1)^i;
+
+s.t. eq{i in 1..n} : n - sum{j in 1..n} cos(x[j]) + i*(1-cos(x[i])) - sin(x[i]) = 0;
+
+option solver knitro;
+option knitro_options "outlev=2 feastol=0 multistart=1";
+
+solve;
+
+display x;