From 6e4bad80f8cd8ce60de67332298c88e379afcbad Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Thu, 1 Aug 2013 16:40:07 -0400
Subject: [PATCH] Add cl.array.diff

---
 pyopencl/array.py       | 27 +++++++++++++++++++++++++--
 pyopencl/elementwise.py | 10 ++++++++++
 test/test_array.py      | 16 ++++++++++++++++
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/pyopencl/array.py b/pyopencl/array.py
index 7f955687..0bede1e6 100644
--- a/pyopencl/array.py
+++ b/pyopencl/array.py
@@ -1573,7 +1573,7 @@ def arange(queue, *args, **kwargs):
 # }}}
 
 
-# {{{ take/put
+# {{{ take/put/concatenate/diff
 
 @elwise_kernel_runner
 def _take(result, ary, indices):
@@ -1840,6 +1840,29 @@ def concatenate(arrays, axis=0, queue=None, allocator=None):
 
     return result
 
+
+@elwise_kernel_runner
+def _diff(result, array):
+    return elementwise.get_diff_kernel(array.context, array.dtype)
+
+
+def diff(array, queue=None, allocator=None):
+    """
+    .. versionadded:: 2013.2
+    """
+
+    if len(array.shape) != 1:
+        raise ValueError("multi-D arrays are not supported")
+
+    n, = array.shape
+
+    queue = queue or array.queue
+    allocator = allocator or array.allocator
+
+    result = empty(queue, (n-1,), array.dtype, allocator=allocator)
+    _diff(result, array, queue=queue)
+    return result
+
 # }}}
 
 
@@ -1864,7 +1887,7 @@ def if_positive(criterion, then_, else_, out=None, queue=None):
 
     if out is None:
         out = empty_like(then_)
-    _if_positive(out, criterion, then_, else_)
+    _if_positive(out, criterion, then_, else_, queue=queue)
     return out
 
 
diff --git a/pyopencl/elementwise.py b/pyopencl/elementwise.py
index 8d6941d5..5878b89c 100644
--- a/pyopencl/elementwise.py
+++ b/pyopencl/elementwise.py
@@ -883,6 +883,16 @@ def get_binary_func_kernel(context, func_name, x_dtype, y_dtype, out_dtype):
         name="%s_kernel" % func_name)
 
 
+@context_dependent_memoize
+def get_diff_kernel(context, dtype):
+    return get_elwise_kernel(context, [
+            VectorArg(dtype, "result", with_offset=True),
+            VectorArg(dtype, "array", with_offset=True),
+            ],
+            "result[i] = array[i+1] - array[i]",
+            name="diff")
+
+
 @context_dependent_memoize
 def get_if_positive_kernel(context, crit_dtype, dtype):
     return get_elwise_kernel(context, [
diff --git a/test/test_array.py b/test/test_array.py
index e3258fb9..3125ac69 100644
--- a/test/test_array.py
+++ b/test/test_array.py
@@ -1,4 +1,5 @@
 #! /usr/bin/env python
+from __future__ import division
 
 __copyright__ = "Copyright (C) 2009 Andreas Kloeckner"
 
@@ -528,6 +529,21 @@ def test_view(ctx_factory):
     view = a_dev.view(np.int16)
     assert view.shape == (8, 32) and view.dtype == np.int16
 
+
+def test_diff(ctx_factory):
+    context = ctx_factory()
+    queue = cl.CommandQueue(context)
+
+    from pyopencl.clrandom import rand as clrand
+
+    l = 20000
+    a_dev = clrand(queue, (l,), dtype=np.float32)
+    a = a_dev.get()
+
+    err = la.norm(
+            (cl.array.diff(a_dev).get() - np.diff(a)))
+    assert err < 1e-4
+
 # }}}
 
 
-- 
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