MAINT: signal: bilinear_zpk array API

Author: ev-br

scipy/signal/_filter_design.py

@@ -2864,8 +2864,11 @@ def bilinear_zpk(z, p, k, fs):
     >>> plt.ylabel('Amplitude [dB]')
     >>> plt.grid(True)
     """
-    z = atleast_1d(z)
-    p = atleast_1d(p)
+    xp = array_namespace(z, p)
+
+    z, p = map(xp.asarray, (z, p))
+    z = xpx.atleast_nd(z, ndim=1, xp=xp)
+    p = xpx.atleast_nd(p, ndim=1, xp=xp)
 
     fs = _validate_fs(fs, allow_none=False)
 
@@ -2878,10 +2881,10 @@ def bilinear_zpk(z, p, k, fs):
     p_z = (fs2 + p) / (fs2 - p)
 
     # Any zeros that were at infinity get moved to the Nyquist frequency
-    z_z = append(z_z, -ones(degree))
+    z_z = xp.concat((z_z, -xp.ones(degree)))
 
     # Compensate for gain change
-    k_z = k * real(prod(fs2 - z) / prod(fs2 - p))
+    k_z = k * xp.real(xp.prod(fs2 - z) / xp.prod(fs2 - p))
 
     return z_z, p_z, k_z
 

scipy/signal/tests/test_filter_design.py

@@ -1614,19 +1614,25 @@ def test_basic(self, xp):
 
 class TestBilinear_zpk:
 
-    def test_basic(self):
-        z = [-2j, +2j]
-        p = [-0.75, -0.5-0.5j, -0.5+0.5j]
+    def test_basic(self, xp):
+        z = xp.asarray([-2j, +2j])
+        p = xp.asarray([-0.75, -0.5-0.5j, -0.5+0.5j])
         k = 3
 
         z_d, p_d, k_d = bilinear_zpk(z, p, k, 10)
 
-        xp_assert_close(sort(z_d), sort([(20-2j)/(20+2j), (20+2j)/(20-2j),
-                                         -1]))
-        xp_assert_close(sort(p_d), sort([77/83,
-                                         (1j/2 + 39/2) / (41/2 - 1j/2),
-                                         (39/2 - 1j/2) / (1j/2 + 41/2), ]))
-        xp_assert_close(k_d, 9696/69803)
+        xp_assert_close(
+            _sort_cmplx(z_d, xp=xp),
+            _sort_cmplx([(20-2j) / (20+2j), (20+2j) / (20-2j), -1], xp=xp)
+        )
+        xp_assert_close(
+            _sort_cmplx(p_d, xp=xp),
+            _sort_cmplx(
+                [77/83, (1j/2 + 39/2) / (41/2 - 1j/2), (39/2 - 1j/2) / (1j/2 + 41/2)],
+                xp=xp
+            )
+        )
+        assert math.isclose(k_d, 9696/69803)
 
 
 class TestPrototypeType: