sxjscience commented on issue #17989: [Gradient Addto] Very serious bug of grad_req='add' URL: https://github.com/apache/incubator-mxnet/issues/17989#issuecomment-610219553 Just verified that there is no problem when `ctx=mx.cpu()` . Also, I've found a simpler script to reproduce the problem: ```python import mxnet as mx import numpy as np mx.npx.set_np() for ctx in [mx.cpu(), mx.gpu()]: for nrepeat in range(1, 10): stored_grad = dict() for grad_req in ['write', 'add']: a = mx.np.array(1, ctx=ctx) b = mx.np.array(2, ctx=ctx) if grad_req == 'write': a.attach_grad(grad_req='write') elif grad_req == 'add': a.attach_grad(grad_req='add') a.grad[()] = 0 with mx.autograd.record(): for _ in range(nrepeat): b = b * a b.backward() stored_grad[grad_req] = a.grad.asnumpy() print('ctx={}, nrepeat={}, write={}, add={}'.format(ctx, nrepeat, stored_grad['write'], stored_grad['add'])) ``` Result: ``` ctx=cpu(0), nrepeat=1, write=2.0, add=2.0 ctx=cpu(0), nrepeat=2, write=4.0, add=4.0 ctx=cpu(0), nrepeat=3, write=6.0, add=6.0 ctx=cpu(0), nrepeat=4, write=8.0, add=8.0 ctx=cpu(0), nrepeat=5, write=10.0, add=10.0 ctx=cpu(0), nrepeat=6, write=12.0, add=12.0 ctx=cpu(0), nrepeat=7, write=14.0, add=14.0 ctx=cpu(0), nrepeat=8, write=16.0, add=16.0 ctx=cpu(0), nrepeat=9, write=18.0, add=18.0 ctx=gpu(0), nrepeat=1, write=2.0, add=2.0 ctx=gpu(0), nrepeat=2, write=4.0, add=4.0 ctx=gpu(0), nrepeat=3, write=6.0, add=6.0 ctx=gpu(0), nrepeat=4, write=8.0, add=8.0 ctx=gpu(0), nrepeat=5, write=10.0, add=62.0 ctx=gpu(0), nrepeat=6, write=12.0, add=126.0 ctx=gpu(0), nrepeat=7, write=14.0, add=254.0 ctx=gpu(0), nrepeat=8, write=16.0, add=16.0 ctx=gpu(0), nrepeat=9, write=18.0, add=18.0 ```
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