Fix bug 4678

Author: gajennings

OpenProblemLibrary/TCNJ/TCNJ_VectorEquations/problem7.pg

@@ -35,6 +35,7 @@ Context("Numeric");
 $v01 = non_zero_random(-5,5,2);
 $v02 = random(-5,5,1);
 $v03 = non_zero_random(-5,5,1);
+$a1 = Matrix([[$v01],[$v02],[$v03]]);
 
 $mult = non_zero_random(-2,2,1);
 $d1 = non_zero_random(-3,3,1);
@@ -43,21 +44,24 @@ $d2 = non_zero_random(-3,3,1);
 $v11 = $mult*$v01;
 $v12 = $mult*$v02+$d1;
 $v13 = $mult*$v03+$d2;
+$a2 = Matrix([[$v11],[$v12],[$v13]]);
 
 $mult2 = non_zero_random(-2,2,1);
 $mult3 = random(-2,2,1);
 $d3 = non_zero_random(-5,5,1);
 $v21 = $mult2*$v01+$mult3*$v11;
 $v22 = $mult2*$v02+$mult3*$v12;
 $v23 = $mult2*$v03+$mult3*$v13+$d3;
+$a3 = Matrix([[$v21],[$v22],[$v23]]);
 
 $A = Matrix([[$v01, $v11, $v21],[$v02, $v12, $v22],[$v03, $v13, $v23]]);
 
-$b1 = random(-6,6,2);
-$b2 = random(-5,5,1);
-$b3 = random(-5,5,1);
-
-$b = Matrix([[$b1],[$b2],[$b3]]);
+do {
+  $b1 = random(-6,6,2);
+  $b2 = random(-5,5,1);
+  $b3 = random(-5,5,1);
+  $b = Matrix([[$b1],[$b2],[$b3]]);
+} until ($b != $a1 && $b != $a2 && $b != $a3);
 
 $ans1 = 3;
 $ans2 = -1;