Add leading_coefficient to fmpz_poly and fmpq_poly

Author: oscarbenjamin

src/flint/test/test_all.py

@@ -3193,11 +3193,7 @@ def test_factor_poly_mpoly():
 
     def factor(p):
         coeff, factors = p.factor()
-        try:
-            lc = p.leading_coefficient()
-        except AttributeError:
-            # XXX: Not all univariate types have a leading_coefficient method.
-            lc = p[0]
+        lc = p.leading_coefficient()
         assert type(coeff) is type(lc)
         assert isinstance(factors, list)
         assert all(isinstance(f, tuple) for f in factors)

src/flint/types/fmpq_poly.pyx

@@ -176,6 +176,24 @@ cdef class fmpq_poly(flint_poly):
     def is_one(self):
         return <bint>fmpq_poly_is_one(self.val)
 
+    def leading_coefficient(self):
+        """
+        Returns the leading coefficient of the polynomial.
+
+        >>> f = fmpq_poly([1, 2, 3])
+        >>> f
+        3*x^2 + 2*x + 1
+        >>> f.leading_coefficient()
+        3
+        """
+        cdef fmpq x
+        cdef slong d
+        d = fmpq_poly_degree(self.val)
+        x = fmpq.__new__(fmpq)
+        if d >= 0:
+            fmpq_poly_get_coeff_fmpq(x.val, self.val, d)
+        return x
+
     def __call__(self, other):
         t = any_as_fmpz(other)
         if t is not NotImplemented:

src/flint/types/fmpz_poly.pyx

@@ -144,6 +144,26 @@ cdef class fmpz_poly(flint_poly):
     def is_one(self):
         return <bint>fmpz_poly_is_one(self.val)
 
+    def leading_coefficient(self):
+        """
+        Returns the leading coefficient of the polynomial.
+
+        >>> f = fmpz_poly([1, 2, 3])
+        >>> f
+        3*x^2 + 2*x + 1
+        >>> f.leading_coefficient()
+        3
+        """
+        cdef fmpz x
+        cdef slong d
+        d = fmpz_poly_degree(self.val)
+        if d < 0:
+            x = fmpz.__new__(fmpz)
+        else:
+            x = fmpz.__new__(fmpz)
+            fmpz_poly_get_coeff_fmpz(x.val, self.val, d)
+        return x
+
     def __call__(self, other):
         t = any_as_fmpz(other)
         if t is not NotImplemented: