polynomial: fix printing.

include/roboptim/trajectory/polynomial.hxx

@@ -94,17 +94,22 @@ namespace trajectory
 	    > std::numeric_limits<value_type>::epsilon ())
 	  {
 	    if (printed_before)
-	      o << " + ";
-	    o << coefs_[idx] << " * x**" << idx;
+	      o << ((coefs_[idx] >= 0.) ? " + " : " - ")
+	        << std::abs (coefs_[idx]);
+      else
+	      o << coefs_[idx];
+      o << " * x**" << idx;
 	    printed_before = true;
 	  }
       }
     if (std::abs (coefs_[0])
         > std::numeric_limits<value_type>::epsilon ())
       {
 	if (printed_before)
-	  o << " + ";
-	o << coefs_[0];
+	      o << ((coefs_[0] >= 0.) ? " + " : " - ")
+	        << std::abs (coefs_[0]);
+  else
+	      o << coefs_[0];
       }
     else if (!printed_before)
       {
@@ -115,9 +120,9 @@ namespace trajectory
     {
       if (std::abs (t0_)
           > std::numeric_limits<value_type>::epsilon ())
-        o << " (x = t - " << t0_ << ")";
+	      o << " (x = t - " << t0_ << ")";
       else
-        o << " (x = t)";
+	      o << " (x = t)";
     }
 
     return o;

tests/polynomial.cc

@@ -516,6 +516,10 @@ void test_print ()
   poly3_t null (1., params);
   (*output) << null << std::endl;
 
+  params[0] = -42;
+  poly3_t negative_constant (2., params);
+  (*output) << negative_constant << std::endl;
+
   params[0] = 42;
   poly3_t constant (2., params);
   (*output) << constant << std::endl;
@@ -527,6 +531,18 @@ void test_print ()
   poly3_t linear2 (3., params);
   (*output) << linear2 << std::endl;
 
+  params[0] = -42;
+  poly3_t linear3 (0., params);
+  (*output) << linear3 << std::endl;
+
+  params[1] = -1;
+  poly3_t linear4 (3., params);
+  (*output) << linear4 << std::endl;
+
+  params[0] = 42;
+  poly3_t linear5 (3., params);
+  (*output) << linear5 << std::endl;
+
   std::cout << output->str () << std::endl;
 
   BOOST_CHECK (output->match_pattern ());

tests/polynomial.stdout

@@ -1,4 +1,8 @@
 0
+-42
 42
 1 * x**1 + 42 (x = t)
 1 * x**1 + 42 (x = t - 3)
+1 * x**1 - 42 (x = t)
+-1 * x**1 - 42 (x = t - 3)
+-1 * x**1 + 42 (x = t - 3)