error value equal to zero when taking a ratio
CITESmike2018 opened this issue · comments
Hi,
I get an error equal to zero when I do the ratio x/x, but if x is assigned a value and y the same value the ratio of x/y is the correct answer. See screenshot:
This isn't a bug but a feature. x is exactly the same thing as x and there is no doubt that x/x is equal to 1, so the uncertainty must be 0. y instead is an independent measure which accidentally happens to have yielded the same value and uncertainty as x, but it's fundamentally something different.
If the fact that x is the same thing as x wasn't taken into account, this wouldn't be possible
julia> x = 1 ± 0.5
1.0 ± 0.5
julia> y = 1 ± 0.5
1.0 ± 0.5
julia> x + x
2.0 ± 1.0
julia> 2 * x
2.0 ± 1.0
julia> x + y
2.0 ± 0.71x + x would return the same as x + y, which is different from 2 * x, which is totally flawed.
This is also extensively documented in the manual, see for example:
- https://juliaphysics.github.io/Measurements.jl/v2.3/usage/#Usage-1, in particular the "Note" box and the "Correlation Between Variables" section;
- https://juliaphysics.github.io/Measurements.jl/v2.3/examples/#Correlation-Between-Variables-1.