Add np.outer for secure arrays.

Author: lschoe

demos/np_lpsolver.py

@@ -202,7 +202,7 @@ async def main():
         pp_inv = 1 / previous_pivot
         p_col = p_col * pp_inv - p_row_index
         p_row = p_row_index @ T + previous_pivot * p_col_index
-        T = T * (pivot * pp_inv) - p_col.reshape(len(p_col), 1) @ p_row.reshape(1, len(p_row))    # consider np.gauss
+        T = T * (pivot * pp_inv) - np.outer(p_col, p_row)
         previous_pivot = pivot
 
     mx = await mpc.output(T[0, -1])

demos/np_lpsolverfxp.py

@@ -178,14 +178,14 @@ async def main():
         cobasis += delta * p_col_index
         basis -= delta * p_row_index
 
-        # update tableau Tij = Tij - (Til - bool(i==k))/Tkl * (Tkj + bool(j==l))
+        # update tableau Tij = Tij - (Til - bool(i==k))/Tkl *outer (Tkj + bool(j==l))
         p_col_index = np.concatenate((p_col_index, np.array([0])))
         p_row_index = np.concatenate((np.array([0]), p_row_index))
         p_col_index.integral = True
         p_row_index.integral = True
         p_col = (p_col - p_row_index) / pivot
         p_row = p_row_index @ T + p_col_index
-        T -= p_col.reshape(len(p_col), 1) @ p_row.reshape(1, len(p_row))
+        T -= np.outer(p_col, p_row)
 
     mx = await mpc.output(T[0,  -1])
     rel_error = (mx - exact_max) / exact_max

mpyc/runtime.py

@@ -2168,6 +2168,43 @@ async def np_matmul(self, A, B):
                 C = self.np_trunc(stype(C, shape=shape))
         return C
 
+    @mpc_coro
+    async def np_outer(self, a, b):
+        """Outer product of vectors a and b.
+
+        Input arrays a and b are flattened if not already 1d.
+        """
+        sha = isinstance(a, self.SecureObject)
+        shb = isinstance(b, self.SecureObject)
+        stype = type(a) if sha else type(b)
+        shape = (a.size, b.size)
+        f = stype.frac_length
+        if not f:
+            rettype = (stype, shape)
+        else:
+            a_integral = a.integral
+            b_integral = b.integral
+            rettype = (stype, a_integral and b_integral, shape)
+            # TODO: handle a or b public integral value
+        await self.returnType(rettype)
+
+        if a is b:
+            a = b = await self.gather(a)
+        elif sha and shb:
+            a, b = await self.gather(a, b)
+        elif sha:
+            a = await self.gather(a)
+        else:
+            b = await self.gather(b)
+        c = np.outer(a, b)  # NB: flattens a and/or b
+        if f and (a_integral or b_integral):
+            c >>= f  # NB: in-place rshift
+        if sha and shb:
+            c = self._reshare(c)
+        if f and not a_integral and not b_integral:
+            c = self.np_trunc(stype(c, shape=shape))
+        return c
+
     @mpc_coro_no_pc
     async def np_getitem(self, a, key):
         """SecureArray a, index/slice key."""

tests/test_runtime.py

@@ -46,6 +46,7 @@ def test_secint_array(self):
         d = np.stack((c, c, c))
         np.assertEqual(mpc.run(mpc.output(c @ d)), a @ b)
         np.assertEqual(mpc.run(mpc.output(d @ d)), b @ b)
+        np.assertEqual(mpc.run(mpc.output(np.outer(c, c))), np.outer(a, a))
         np.assertEqual(mpc.run(mpc.output(np.stack((c, c), axis=1))), np.stack((a, a), axis=1))
         np.assertEqual(mpc.run(mpc.output(np.block([[c, c], [c, c]]))), np.block([[a, a], [a, a]]))
         np.assertEqual(mpc.run(mpc.output(np.block([[secint(9), -1]]))), np.block([[9, -1]]))
@@ -141,6 +142,7 @@ def test_secfxp_array(self):
         np.assertEqual(mpc.run(mpc.output(mpc.run(mpc.transfer(c, senders=0)))), a)
         np.assertEqual(mpc.run(mpc.output(mpc.input(c, senders=0))), a)
         np.assertEqual(mpc.run(mpc.output(mpc._reshare(c) @ c)), a @ a)
+        np.assertEqual(mpc.run(mpc.output(np.outer(c, c))), np.outer(a, a))
         b = mpc.run(mpc.output(c * c))
         np.assertEqual(b, a * a)
         self.assertTrue(np.issubdtype(b.dtype, np.floating))
@@ -162,6 +164,7 @@ def test_secfld_array(self):
         c = secfld.array(a)
         np.assertEqual(mpc.run(mpc.np_is_zero_public(c.flatten())), [False, True, True, False])
         self.assertEqual(mpc.run(mpc.output(c.flatten().tolist())), [-1, 0, 0, -1])
+        np.assertEqual(mpc.run(mpc.output(np.outer(c, c))), np.outer(a, a))
         self.assertEqual(len(c), 1)
         self.assertEqual(len(c.T), 2)
         self.assertTrue(bool(c))