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docs: complex character added to the "Quantity character" chapter
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mpusz committed Jan 24, 2025
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Expand Up @@ -120,13 +120,14 @@ results in the `derived_dimension<isq::dim_length, per<isq::dim_time>>` type.
different [characters](../../appendix/glossary.md#character):

- scalar,
- complex,
- vector,
- tensor.

The quantity character in the **mp-units** library is implemented with the `quantity_character` enumeration:

```cpp
enum class quantity_character { scalar, vector, tensor };
enum class quantity_character { scalar, complex, vector, tensor };
```
!!! info
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8 comments on commit 7ea23dd

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Does complex fit into these exclusive characters?
Can something not be (scalar and complex) or
(vector and complex)?

@mpusz
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@mpusz mpusz commented on 7ea23dd Jan 25, 2025

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I do not know. Do you know an example of a vector complex quantity? I need complex to model things like complex power as mentioned in the last paragraph of my latest article.

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A tensor could always be of vector elements.
So far, mp-units uses these for concepts and customization points,
and doesn't concern itself with the number's element, unlike its scalar.

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@mpusz mpusz commented on 7ea23dd Jan 25, 2025 •
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To be exact, quantity_character specifies which operations can or can't be performed on a given quantity.

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@Spammed Spammed commented on 7ea23dd Jan 25, 2025 •
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Do you know an example of a vector complex quantity?

I have no dealings with these type of quantities, but they should exist.
For example, a mechanical or electrical impedance (represented as a complex-valued quantity) could be directional, so it should be possible to describe it as a vector of complex quantities.
Presumably there is also something like a complex-valued stress-strain tensor. Why not?

[real or complex]-valued and [scalar or vector or tensor]-like are different properties that are not mutually exclusive.

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@mpusz mpusz commented on 7ea23dd Jan 26, 2025

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That is a good feedback. Thank you! We need to think about how to model this. Maybe a quantity character should be a struct of enums?

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@Spammed Spammed commented on 7ea23dd Jan 26, 2025 •
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Why isn't complex (not to say std::complex<...>) just another number type?
So, belongs in a line with byte, integer, float, double, ...

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@mpusz mpusz commented on 7ea23dd Jan 26, 2025 •
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Yes and no. Complex quantities should expose additional interfaces like real(), imag() and mod(). A result of those is another specific quantity. As I wrote in my article:

For example, in the case of complex quantities, we want to ensure that only:

  • the real part of a complex power is assigned to an active power,
  • the imaginary part of a complex power is assigned to an reactive power,
  • the modulus of a complex power is assigned to an apparent power.

Mixing the above is a fatal error in power systems engineering.

Also, a complex power should be created from active and reactive powers passed in that order and not the other way around.

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