Hello Eugene,
I have attached a minimum example using the exact typedefs I use in my project.
I am compiling on MacOS with an up-to-date system clang, if that makes any difference.
Best wishes,
Toby
From: Eugene Zhulenev <ezhulenev@xxxxxxxxxx>
Reply to: "eigen@xxxxxxxxxxxxxxxxxxx" <eigen@xxxxxxxxxxxxxxxxxxx>
Date: Tuesday, 17 December 2019 at 19:31
To: "eigen@xxxxxxxxxxxxxxxxxxx" <eigen@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [eigen] Returning Tensor Expressions
Hello,
I am trying to write a finite difference function for Eigen::Tensors. Currently I am using a lambda:
auto diff = [](Eigen::Tensor<std::complex<float>,
3>
const
&a,
Eigen::Index
const
d) {
Dims3 const sz{a.dimension(0)
- 2,
a.dimension(1)
- 2,
a.dimension(2)
- 2};
Dims3 const st1{1,
1,
1};
Dims3 fwd{1,
1,
1};
Dims3 bck{1,
1,
1};
fwd[d] =
2;
bck[d] =
0;
return (a.slice(fwd,
sz) - a.slice(bck,
sz)) / a.slice(st1,
sz).constant(2.f);
};
This works okay. However, I would like to do two things:
1 – Change this from a lambda into a free function. What should the return type of the function be, so that it returns the _expression_/operation and does not evaluate the tensor
into a temporary?
2 – I would prefer to pass in a TensorRef, so I can pass in a .chip() from a 4D tensor without a temporary. When I try to do this with the current lambda, and I am assigning to
a slice, e.g.
b.chip<3>(0).slice(st1,
sz) = diff(a,
0);
I get the following error:
TensorRef.h:413:51: error: cannot initialize return object of type 'Eigen::TensorEvaluator<const Eigen::TensorRef<Eigen::Tensor<std::__1::complex<float>, 3, 0, long> >, Eigen::ThreadPoolDevice>::Scalar
*' (aka 'std::__1::complex<float> *') with an rvalue of type 'const Eigen::TensorRef<Eigen::Tensor<std::__1::complex<float>, 3, 0, long> >::Scalar *' (aka 'const std::__1::complex<float> *')
This appears to be complaining that I can’t assign a `const std::complex<float> *` to a `std::complex<float> *`?
Can you create a minimal repro for this, can't quite figure out how you try to use TensorRef, and what is the source of `const` in the _expression_. Looks like a bug somewhere in typedefs.
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