larroy commented on a change in pull request #14992: [MXNET-978] Support higher order gradient for `log`. URL: https://github.com/apache/incubator-mxnet/pull/14992#discussion_r288364928
########## File path: src/operator/tensor/elemwise_unary_op_basic.cc ########## @@ -1069,13 +1069,73 @@ The storage type of ``log2`` output is always dense .set_attr<nnvm::FGradient>("FGradient", ElemwiseGradUseIn{"_backward_log2"}); MXNET_OPERATOR_REGISTER_BINARY_WITH_SPARSE_CPU_DR(_backward_log, - unary_bwd<mshadow_op::log_grad>); + unary_bwd<mshadow_op::log_grad>) +.set_attr<nnvm::FGradient>("FGradient", + [](const nnvm::NodePtr& n, const std::vector<nnvm::NodeEntry>& ograds) { + // For f(x) -> f = log + // f''(x) = -1 * (f'(x) * f'(x)) + auto gx = nnvm::NodeEntry{n}; + auto ggx_mid = MakeNode("elemwise_mul", n->attrs.name + "_backward_mid_grad_grad", + {gx, gx}, nullptr, &n); + auto ggx = MakeNode("negative", n->attrs.name + "_backward_grad_grad", + {nnvm::NodeEntry{ggx_mid}}, nullptr, &n); + + std::vector<nnvm::NodeEntry> ret; + + ret.emplace_back(MakeNode("elemwise_mul", n->attrs.name + "_backward_grad_grad", + {ograds[0], gx}, nullptr, &n)); + ret.emplace_back(MakeNode("elemwise_mul", n->attrs.name + "_backward_grad_grad_inp", + {ograds[0], nnvm::NodeEntry{ggx}}, nullptr, &n)); + return ret; + }); MXNET_OPERATOR_REGISTER_BINARY_WITH_SPARSE_CPU_DR(_backward_log10, - unary_bwd<mshadow_op::log10_grad>); + unary_bwd<mshadow_op::log10_grad>) +.set_attr<nnvm::FGradient>("FGradient", + [](const nnvm::NodePtr& n, const std::vector<nnvm::NodeEntry>& ograds) { + // For f(x) -> f = log10 + // f'(x) = 1 / (log(10) * x) + // f''(x) = -1 * (f'(x) * 1/x) + auto gx = nnvm::NodeEntry{n, 0, 0}; Review comment: Why don't we follow the same pattern as in the natural logarithm? ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services