[math] fix brainpy.math.scan (#604)

brainpy/_src/math/object_transform/controls.py

@@ -940,6 +940,8 @@ def scan(
 ):
   """``scan`` control flow with :py:class:`~.Variable`.
 
+  Similar to ``jax.lax.scan``.
+
   .. versionadded:: 2.4.7
 
   All returns in body function will be gathered
@@ -999,7 +1001,7 @@ def scan(
           rets = jax.eval_shape(transform, init, operands)
     cache_stack(body_fun, dyn_vars)  # cache
     if current_transform_number():
-      return rets[1]
+      return rets[0][1], rets[1]
     del rets
 
   transform = _get_scan_transform(body_fun, dyn_vars, bar, progress_bar, remat, reverse, unroll)

brainpy/_src/math/object_transform/tests/test_controls.py

@@ -1,14 +1,11 @@
 # -*- coding: utf-8 -*-
-import sys
 import tempfile
 import unittest
 from functools import partial
 
 import jax
-from jax import vmap
-
 from absl.testing import parameterized
-from jax._src import test_util as jtu
+from jax import vmap
 
 import brainpy as bp
 import brainpy.math as bm
@@ -147,6 +144,25 @@ def f(carray, x):
     expected = bm.expand_dims(expected, axis=-1)
     self.assertTrue(bm.allclose(outs, expected))
 
+  def test2(self):
+    a = bm.Variable(1)
+
+    def f(carray, x):
+      carray += x
+      a.value += 1.
+      return carray, a
+
+    @bm.jit
+    def f_outer(carray, x):
+      carry, outs = bm.scan(f, carray, x, unroll=2)
+      return carry, outs
+
+    carry, outs = f_outer(bm.zeros(2), bm.arange(10))
+    self.assertTrue(bm.allclose(carry, 45.))
+    expected = bm.arange(1, 11).astype(outs.dtype)
+    expected = bm.expand_dims(expected, axis=-1)
+    self.assertTrue(bm.allclose(outs, expected))
+
 
 class TestCond(unittest.TestCase):
   def test1(self):
@@ -234,7 +250,6 @@ def F2(x):
     self.assertTrue(bm.grad(F2)(9.0) == 18.)
     self.assertTrue(bm.grad(F2)(11.0) == 1.)
 
-
   def test_grad2(self):
     def F3(x):
       return bm.ifelse(conditions=(x >= 10, x >= 0),
@@ -519,6 +534,3 @@ def body(a):
     file.seek(0)
     out6 = file.read().strip()
     self.assertTrue(out5 == out6)
-
-
-

docs/apis/brainpy.math.oo_transform.rst

@@ -60,6 +60,7 @@ Object-oriented Transformations
    ifelse
    for_loop
    while_loop
+   scan
    jit
    cls_jit
    to_object