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Conversion to/from complex storage types is wrong #452

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mkalte666 opened this issue Jan 15, 2024 · 0 comments · May be fixed by #453
Open

Conversion to/from complex storage types is wrong #452

mkalte666 opened this issue Jan 15, 2024 · 0 comments · May be fixed by #453

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@mkalte666
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mkalte666 commented Jan 15, 2024 •
edited

Heya, i have run into the following issue:

Lets assume a complex impedance like Z = (123 + 321j) * ohm

use uom::fmt::DisplayStyle;
use uom::si::complex64::ElectricalResistance;
use uom::si::electrical_resistance::ohm;
use uom::num_complex::Complex64;

fn main() {
    let n = Complex64::new(123.0,321.0);
    let unit = ElectricalResistance::new::<ohm>(n);
    println!("{} -> {}", n, unit.into_format_args(ohm,DisplayStyle::Abbreviation));
    assert_eq!(n,unit.get::<ohm>());
}

this fails:

123+321i -> 343.7586362551492+0i Ω
thread 'main' panicked at src\main.rs:10:5:
assertion `left == right` failed
  left: Complex { re: 123.0, im: 321.0 }
 right: Complex { re: 343.7586362551492, im: 0.0 }

343.7586362551492 being the norm of the number.

I have looked at the implementing PR: while i would expect the pure unit conversion factor to be a floating point type, the actual conversion operation must be in the complex numbers, otherwise the operation is one-way (there are infinite solutions to |z|^2 = re^2 + im^2 for a single given z; think vectors describing a circle of radius z).

Im gonna have a go at either understanding where im wrong in my assumptions, or fixing this, as i really want complex impedance :D
@mkalte666 mkalte666 changed the title Conversion to/from complex storage types is weong Conversion to/from complex storage types is wrong Jan 15, 2024
mkalte666 added a commit to mkalte666/uom that referenced this issue Jan 15, 2024
@mkalte666
Conversion now has both a value and a factor type
b285dc8 
Initially, `ConversionFactor` and thus `Conversion::T` requred `PartialEq`.
This makes sense for the conversion factor itself (i.e. scaling across
units), however it breaks once you introduce complex numbers.

Those can *still* be scaled just like normal numbers - you essentially
just increase or decrese a vector length, but the conversion function
cannot compare them - "Z_1 < Z_2" is not trivially decidable.

It is, however, also not needed - unit scales are just that - scalars
that scale. And those can be easily compared.

This commit seperates `Conversion::T` into `Conversion::VT` and
`Conversion::T` and moves the `PartialEq` requirements from
`ConversionFactor` into `Conversion::TT` directly.

This requires a lot of trait bounds added down the line, so im not 100%
that this does not break anything down the line.

There might be a nicer way to go about this, but i haven't found any.

closes iliekturtles#452
@mkalte666 mkalte666 linked a pull request Jan 15, 2024 that will close this issue
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Conversion now has both a value and a factor type mkalte666/uom
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@mkalte666