Allow ability to delete default units

[Virushaan]

Describe the bug
Currently a scalar divided by a time unit such as 5/seconds will get converted into hertz 5Hz. However, for my usecase, hertz(hz) doesn't make sense to convert into. Ideally it would be possible to keep the evaluated value as 5/seconds and not simplify any further.

I have tried
math.Unit.deleteUnit('Hz')
and
delete math.Unit.UNITS['hertz'];
and neither seemed to have any impact. Open to any thoughts or ideas! Thanks in advance :)

[dvd101x]

I've found a few possibilities

5 / s to s^-1      # 5 s^-1
a = unit(5, "1/s") # 5 s^-1
a + 1/s            # 6 s^-1

Another possibility is to use createUnit with an override. So you could assign Hz to something that doesn't makes sense.
math.createUnit('Hz', '1 m^100', {override: true}) but I don't know if this one works at the level you need.

Maybe there is a trick to your use case, can you show your code that converts 5 / seconds to 5 Hz? Maybe it's possible to trick the system.

[gwhitney]

I agree with @dvd101x; the "Hz" unit is just a synonym for 1/s, it's not truly a "simplification" of it. It may be used for input/output, but it doesn't affect the underlying unit value. In what code exactly is "Hz" getting in your way?

And indeed, in JavaScript rather than MaJE (the MathJs Expressions language) we have

const oneway = math.evaluate('5/s')
const otherway = math.unit(5, '1/s')
console.log(oneway.format()) // 5 Hz
console.log(otherway.format()) // 5 s^-1
assert.deepStrictEqual(oneway, otherway) // fails, but shows that the _only_
// difference between these two Unit objects is that 
// oneway.skipAutomaticSimplification is false, whereas
// otherway.skipAutomaticSimplification is true.

So if you are handling these units in JavaScript, you could just manually set the skipAutomaticSimplification property to true. If you are handling them in MaJE, then you need to either use the in operator, the to operator, or the two-argument unit function to ensure that you get an object with skipAutomaticSimplification set to true. But in all of these cases, the internal unit calculations will be identical regardless of the value of skipAutomaticSimplification. It's just a matter of display/conversion to string, not of the underlying value.