Fix bug when extrap is float

-Passing in a float for `extrap` caused an error due to some poorly
ordered conditionals and weird jax dtype issues. Should work now.

Resolves #16

interpax/_spline.py

@@ -1104,6 +1104,8 @@ def _parse_ndarg(arg, n):
 def _parse_extrap(extrap, n):
     if isbool(extrap):  # same for lower,upper in all dimensions
         return tuple(extrap for _ in range(2 * n))
+    elif jnp.isscalar(extrap):
+        return tuple(extrap for _ in range(2 * n))
     elif len(extrap) == 2 and jnp.isscalar(extrap[0]):  # same l,h for all dimensions
         return tuple(e for _ in range(n) for e in extrap)
     elif len(extrap) == n and all(len(extrap[i]) == 2 for i in range(n)):
@@ -1140,15 +1142,17 @@ def hiclip(fq, hi):
     def noclip(fq, *_):
         return fq
 
+    # if extrap = True, don't clip. If it's false or numeric, clip to that value
+    # isbool(x) & bool(x) is testing if extrap is True but works for np/jnp bools
     fq = jax.lax.cond(
-        isbool(lo) & lo,
+        isbool(lo) & jnp.asarray(lo).astype(bool),
         noclip,
         loclip,
         fq,
         lo,
     )
     fq = jax.lax.cond(
-        isbool(hi) & hi,
+        isbool(hi) & jnp.asarray(hi).astype(bool),
         noclip,
         hiclip,
         fq,

tests/test_interpolate.py

@@ -613,3 +613,15 @@ def test_ad_interp3d(self):
             # for some reason finite difference gives nan at endpoints so ignore that
             np.testing.assert_allclose(jacf1[1:-1], jacd1[1:-1], rtol=1e-6, atol=1e-6)
             np.testing.assert_allclose(jacf2[1:-1], jacd2[1:-1], rtol=1e-6, atol=1e-6)
+
+
+@pytest.mark.unit
+def test_extrap_float():
+    """Test for extrap being a float, from gh issue #16."""
+    x = jnp.linspace(0, 10, 10)
+    y = jnp.linspace(0, 8, 8)
+    z = jnp.zeros((10, 8)) + 1.0
+    interpol = Interpolator2D(x, y, z, extrap=0.0)
+    np.testing.assert_allclose(interpol(4.5, 5.3), 1.0)
+    np.testing.assert_allclose(interpol(-4.5, 5.3), 0.0)
+    np.testing.assert_allclose(interpol(4.5, -5.3), 0.0)