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See if we can remove mathematically iffy Complex rounding modes #52490

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See if we can remove mathematically iffy Complex rounding modes #52490

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31 changes: 20 additions & 11 deletions base/complex.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -1077,19 +1077,22 @@ end
#Rounding complex numbers
#Requires two different RoundingModes for the real and imaginary components
"""
round(z::Complex[, RoundingModeReal, [RoundingModeImaginary]])
round(z::Complex[, RoundingModeReal, [RoundingModeImaginary]]; digits=0, base=10)
round(z::Complex[, RoundingModeReal, [RoundingModeImaginary]]; sigdigits, base=10)
round(z::Complex[, RoundingMode])
round(z::Complex[, RoundingMode]; digits=0, base=10)
round(z::Complex[, RoundingMode]; sigdigits=0, base=10)
round(z::Complex, RoundingModeReal, RoundingModeImaginary;)
round(z::Complex, RoundingModeReal, RoundingModeImaginary; digits=0, base=10)
round(z::Complex, RoundingModeReal, RoundingModeImaginary; sigdigits, base=10)

Return the nearest integral value of the same type as the complex-valued `z` to `z`,
breaking ties using the specified [`RoundingMode`](@ref)s. The first
[`RoundingMode`](@ref) is used for rounding the real components while the
second is used for rounding the imaginary components.
breaking ties using the specified [`RoundingMode`](@ref)s. When provided a single
[`RoundingMode`](@ref), the mode must be one of `RoundNearest`, `RoundFromZero`, `RoundToZero`,
or `RoundNearestTiesAway`, since these are the modes which do not rely on a total ordering which
the complex numbers lack.


`RoundingModeReal` and `RoundingModeImaginary` default to [`RoundNearest`](@ref),
which rounds to the nearest integer, with ties (fractional values of 0.5)
being rounded to the nearest even integer.
Complex numbers can also be passed two rounding modes, one for the real part and another for
the imaginary part. In this case, the Complex number's components will be rounded seperately
using the provided rounding modes, and combined back into a Complex number.

# Example
```jldoctest
Expand All @@ -1106,7 +1109,13 @@ julia> round(3.14159 + 4.512im; sigdigits = 3)
3.14 + 4.51im
```
"""
function round(z::Complex, rr::RoundingMode=RoundNearest, ri::RoundingMode=rr; kwargs...)
function round(z::Complex, rr::RoundingMode; kwargs...)
if rr in (RoundNearest, RoundFromZero, RoundToZero, RoundNearestTiesAway)
return round(z, rr, rr; kwargs...)
end
error("Rounding Mode $rr not supported for Complex numbers. Use round(z, $rr, $rr)")
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@StefanKarpinski StefanKarpinski Jan 10, 2024

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I would throw and ArgumentError here.

end
function round(z::Complex, rr::RoundingMode, ri::RoundingMode; kwargs...)
Complex(round(real(z), rr; kwargs...),
round(imag(z), ri; kwargs...))
end
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