8000 BUG: Ensure out is returned in einsum. by mattip · Pull Request #11406 · numpy/numpy · GitHub
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BUG: Ensure out is returned in einsum. #11406

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Merged
merged 3 commits into from
Jun 29, 2018
Merged

BUG: Ensure out is returned in einsum. #11406

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d829dc5
BUG: ensure ret is out in einsum
mattip Jun 21, 2018
4f5ada2
check for unlikely error in Assign_Zero
mattip Jun 24, 2018
ae5000f
MAINT: cleanup ret assignment
mattip Jun 27, 2018
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7 changes: 6 additions & 1 deletion numpy/core/src/multiarray/einsum.c.src
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Expand Up @@ -2769,8 +2769,13 @@ PyArray_EinsteinSum(char *subscripts, npy_intp nop,

/* Initialize the output to all zeros and reset the iterator */
ret = NpyIter_GetOperandArray(iter)[nop];
if (PyArray_AssignZero(ret, NULL) < 0) {
goto fail;
}
if (out != NULL) {
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This looks fishy, why do anything to ret if it is simply set to out?

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If the output operand has writeback semantics, NpyIter_GetOperandArray(iter)[nop] is the temporary ndarray created with out as it's base ndarray. Then we zero the temporary data rather than changing out itself. See issue #10956 for the python-level equivalent discussion about what is meant by iter.operand[i] - the temporary ndarray with writeback semantics or the underlying user-created input-ouput ndarray.

Lines 2775-2777 ensure that ret and out point to the same ndarray, as required when using an out kwarg.

ret = out;
}
Py_INCREF(ret);
PyArray_AssignZero(ret, NULL);


/***************************/
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5 changes: 5 additions & 0 deletions numpy/core/tests/test_einsum.py
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Expand Up @@ -730,6 +730,11 @@ def test_small_boolean_arrays(self):
res = np.einsum('...ij,...jk->...ik', a, a, out=out)
assert_equal(res, tgt)

def test_out_is_res(self):
a = np.arange(9).reshape(3, 3)
res = np.einsum('...ij,...jk->...ik', a, a, out=a)
assert res is a

def optimize_compare(self, string):
# Tests all paths of the optimization function against
# conventional einsum
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0