Improve algebraic number to rational

return the true rational when is_rational is true by adding the case
P(X)=den*X-num

src/number/algebraic_number.c

@@ -28,6 +28,7 @@
 #include "polynomial/coefficient.h"
 #include "polynomial/output.h"
 #include "upolynomial/output.h"
+#include "upolynomial/upolynomial.h"
 
 #include "utils/debug_trace.h"
 
@@ -553,6 +554,19 @@ void lp_algebraic_number_to_rational(const lp_algebraic_number_t* a_const, lp_ra
     return;
   }
 
+  if (lp_upolynomial_degree(a_const->f) == 1) {
+    // If degree 1, we're directly rational
+    if(a_const->f->size==2){
+      mpz_neg(&q->_mp_num,&a_const->f->monomials[0].coefficient);
+      mpz_set(&q->_mp_den,&a_const->f->monomials[1].coefficient);
+    } else {
+      /* a_const == 0, is it possible without a_const->f==0? */
+      assert (a_const->f->size<=1);
+      mpq_set_ui(q,0,1);
+    }
+    return;
+  }
+
   // We do the necessary refinement on a copy
   lp_algebraic_number_t a;
   lp_algebraic_number_construct_copy(&a, a_const);