How to use convert a number?

[WG-]

As a first contribution to the project, I thought I would implement rad2deg and deg2rad. However, then I found out mathjs has a unit module. But how does that exactly work? Let say I have a variable x, which I know is in radians, did not explicitly specify it, but I want to convert it to degrees? How can I achieve this? Is there a oneliner? Something like f.unit.to('deg','rad')? In addition, does the result also store the unit in the new variable? Because frankly I do not care about it and most likely it makes all operations after slower, because it takes the unit into account when doing calculations?

[josdejong]

In the expression parser you could do x * rad / deg or create a function yourself like

rad2deg(x) = x * rad / deg
rad2deg(2 * pi) # 360

The equivalent in plain javascript is:

function radToDeg(x) { 
  return math.divide(math.multiply(x, math.unit('rad')), math.unit('deg')) 
}

Or something like:

function radToDeg(x) { 
  return math.unit(x, 'rad').toNumeric('deg') 
}

[WG-]

Okay, but we don't want a dedicated function for this? Such that you can simply call math.radToDeg or math.degToRad?

[josdejong]

Yeah, if there is need for it we can consider it. So far you're the first asking about it :). It's indeed quite a common util function for working with angles.

The idea of using units instead of converting numbers yourself is that you can simply do sin(1.57 rad) and sin(90 deg) so you cannot accidentally make mistakes with units. These sort of issues have literally crashed rockets in the past, it's a dream of mine to get rid of issues these type of issues by offering a system where you can work with units instead of numbers.

[WG-]

You are totally correct that unit issues made rockets crash in the past. But I would prefer to have a simple accesible function for that. I think as well that it is a common util function, which I normally use quiet often in the field of control engineering and digital signal processing. If it is okay I will create those two functions and submit a PR.

[josdejong]

Yes I'm ok with that. I agree that its a very common/handy util function.