Calculate Ax - b numerically

src/test-gradient-trivial.cc

@@ -37,15 +37,8 @@ int main() {
   Functional::SmallVector start = b;
   start *= 17;
 
-  /*
-    j(x)
-    = Ax - b
-    = 17*(6, 9.5) - (1, 2)
-    = (102 - 1, 161.5 - 2)
-  */
-  Functional::SmallVector analytic_descent;
-  analytic_descent[0] = -101;
-  analytic_descent[1] = -159.5;
+  Functional::SmallVector analytic_descent = b;
+  A.mmv(start, analytic_descent);
   Functional::SmallVector numerical_descent;
   J.descentDirection(start, numerical_descent);
   assert(two_distance<dim>(numerical_descent, analytic_descent) < 1e-10);