Fix atomics example

Author: ZzEeKkAa

numba_dpex/examples/kernel/atomic_op.py

@@ -8,20 +8,28 @@
 
 
 @ndpx.kernel
-def atomic_reduction(a):
+def atomic_reduction(a, res):
+    """Summarize all the items in a and writes it into res using atomic.add.
+
+    :param a: array of values to get sum
+    :param res: result where to add all the items from a array. It must be preset to 0.
+    """
     idx = ndpx.get_global_id(0)
-    ndpx.atomic.add(a, 0, a[idx])
+    ndpx.atomic.add(res, 0, a[idx])
 
 
 def main():
     N = 10
-    a = np.arange(N)
+
+    # We are storing sum to the first element
+    a = np.arange(0, N)
+    res = np.zeros(1, dtype=a.dtype)
 
     print("Using device ...")
     print(a.device)
 
-    atomic_reduction[ndpx.Range(N)](a)
-    print("Reduction sum =", a[0])
+    atomic_reduction[ndpx.Range(N)](a, res)
+    print("Reduction sum =", res[0])
 
     print("Done...")