what's differences between dual, real and var #370

shi-yan · 2025-01-24T16:03:25Z

shi-yan
Jan 24, 2025

And when to use which? Can I do std::vector to provide a variable length input to a function?

Thanks,

shi-yan · 2025-01-24T17:19:01Z

shi-yan
Jan 24, 2025
Author

-

I see now that dual is only used for froward mode and var is for the backward mode.

0 replies

NarakuK · 2025-03-19T18:05:37Z

NarakuK
Mar 19, 2025

1.Can I do std::vector to provide a variable length input to a function?
The autodiff library supports custom type inputs. std::vector, as a commonly used dynamic array container in the C++ standard library, can be used to store multiple input values. You can pass std::vector as a function parameter and then operate on these input values within the function.
a toy sample:
real sum_of_squares(const std::vector& x) {
real result = 0.0;
for (const auto& val : x) {
result += val * val;
}
return result;
}

2.what's differences between dual, real and var？
**2.1 var:**The var type is generally used for automatic differentiation in reverse mode. The reverse mode is suitable for situations where there are many input variables and few output variables.
Backpropagation support: Supports the backpropagation algorithm, which first calculates the function value through forward propagation by constructing a calculation graph, and then calculates the derivative through backpropagation from the final result.
Memory management: During the calculation process, intermediate results are recorded for use in backpropagation, which may consume a significant amount of memory.
**2.2 dual:**Both dual and real are used in forward mode. The dual type is mainly designed for efficient calculation of high-order cross derivatives. for example：d⁴u/dx²dydz
**2.3 real:**The real type is optimized for efficient calculation of high-order directional derivatives.for example：d⁴u/dx⁴.
Note that real types usually do not support the calculation of high-order cross derivatives！！！！！

In fact, many times the two can be interchangeable, but as the author mentioned, it is recommended to use them according to the above guidelines because the author has optimized the underlying code for these two different task requirements.

The above is my personal shallow understanding.

0 replies

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

what's differences between dual, real and var #370

Uh oh!

{{title}}

Uh oh!

Replies: 2 comments

Uh oh!

{{title}}

Uh oh!

Uh oh!

{{title}}

Uh oh!

Select a reply

Uh oh!

what's differences between dual, real and var #370

Uh oh!

shi-yan Jan 24, 2025

Replies: 2 comments

Uh oh!

shi-yan Jan 24, 2025 Author

Uh oh!

NarakuK Mar 19, 2025

shi-yan
Jan 24, 2025

shi-yan
Jan 24, 2025
Author

NarakuK
Mar 19, 2025