matteosal opened a new issue #20149:
URL: https://github.com/apache/incubator-mxnet/issues/20149
This program creates a simple operator and runs forward + backward with the
C API, checking for failures:
```
#include <iostream>
#include "mxnet/c_api.h"
#include "nnvm/c_api.h"
#define checkedMXCall(func, ...) \
{ \
if (func(__VA_ARGS__) != 0) { \
printf("MX call %s failed at line %d:\n%s", \
#func, __LINE__, MXGetLastError()); \
exit(1) ; \
} \
}
int main() {
/* Create symbol variables */
SymbolHandle in_sym;
checkedMXCall(MXSymbolCreateVariable, "in", &in_sym);
/* Create symbol */
OpHandle op;
NNGetOpHandle("sin", &op);
SymbolHandle sym;
checkedMXCall(MXSymbolCreateAtomicSymbol, op, 0, nullptr, nullptr, &sym);
checkedMXCall(MXSymbolCompose, sym, "Sin", 1, nullptr, &in_sym);
/* Create NDArray for argument */
int dev_type = 1;
int dev_id = 0;
mx_uint shape[2] = {2, 3};
NDArrayHandle in_arr;
checkedMXCall(MXNDArrayCreate, shape, 2, dev_type, dev_id, 0, 0, &in_arr);
/* Create NDArray for gradient and attach gradient */
NDArrayHandle grad_arr;
checkedMXCall(MXNDArrayCreate, shape, 2, dev_type, dev_id, 0, 0,
&grad_arr);
uint32_t grad_req[1] = {1};
checkedMXCall(MXAutogradMarkVariables, 1, &in_arr, grad_req, &grad_arr);
/* Create cached op */
const char *cachedop_keys[1] = {"static_alloc"};
const char *cachedop_vals[1] = {"true"};
CachedOpHandle cached_op;
checkedMXCall(MXCreateCachedOp, sym, 1, cachedop_keys, cachedop_vals,
&cached_op, true);
/* Set autograd to record */
int dummy_prev;
checkedMXCall(MXAutogradSetIsRecording, 1, &dummy_prev);
/* Run cached op */
int n_outs;
NDArrayHandle *out_arr = nullptr;
const int *dummy_stypes = nullptr;
checkedMXCall(MXInvokeCachedOp, cached_op, 1, &in_arr, dev_type, dev_id,
&n_outs, &out_arr, &dummy_stypes);
/* Check that autograd is recording */
bool res;
checkedMXCall(MXAutogradIsRecording, &res);
std::cout << "IsRecording: " << res << "\n";
/* Create NDArray for outgrad and run backward */
NDArrayHandle outgrad_arr;
checkedMXCall(MXNDArrayCreate, shape, 2, dev_type, dev_id, 0, 0,
&outgrad_arr);
checkedMXCall(MXAutogradBackward, 1, out_arr, &outgrad_arr, true);
return 0;
}
```
The output is:
```
[20:23:58]
/home/matteo/Git/mxnet-build/Build/Linux-x86-64/MKL/mxnet/src/storage/storage.cc:199:
Using Pooled (Naive) StorageManager for CPU
IsRecording: 1
MX call MXAutogradBackward failed at line 65:
MXNetError: Check failed: !AGInfo: :IsNone(*i): Cannot differentiate node
because it is not in a computational graph. You need to set is_recording to
true or use autograd.record() to save computational graphs for backward. If you
want to differentiate the same graph twice, you need to pass retain_graph=True
to backward.
Stack trace:
File
"/home/matteo/Git/mxnet-build/Build/Linux-x86-64/MKL/mxnet/src/imperative/imperative.cc",
line 402
```
Why is `MXAutogradBackward` complaining about autograd recording if
`MXAutogradIsRecording` gives `true`? Am I doing something wrong here?
Thanks
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