Re: [swift-users] Dimensional analysis

[Howard Lovatt via swift-users]

Another feature I would like would be a dimensions wrapper for an array. So
that I can mark all values in the array as having the same units, rather
than mark each individual element as having a particular unit.

It is conceivable that wrapping each element, both performance and memory
wise, is OK depending on implementation. However my experience with
Mathematica's Quantity is that wrapping each element is a significant
overhead. Therefore I would like a dimensioned array.

As an aside. It might be a lot easier to write an array wrapper when we get
Conditional Conformance To Protocols with the improved generics slated for
Swift 4.1. Therefore it might be worth waiting until 4.1. before attempting
a dimensioned array.

  -- Howard.

On 1 December 2016 at 01:17, Maury Markowitz via swift-users <
swift-users@swift.org> wrote:

> Let me add my support for this as well. I am currently using a bridge
> version of:
>
> https://github.com/unixpickle/Expressions
>
> And it works quite well. But I think a pure Swift implementation,
> especially with dimensional analysis, would be useful to a great number of
> people.
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[swift-users] Dimensional analysis

[Rick Mann via swift-users]

My earlier post about converting Decimal to Double was part of a larger effort 
by me to write a calculator app that supports dimensional analysis/unit 
conversions. I've explored some existing libraries on the topic, ranging from 
this one in Common Lisp () 
to this nice-looking C++ header-only implementation 
(). Here's one done in Swift 
(), which has similarities to the 
C++ library.

My calculator allows expressions like this:

1-3/4" x 2 + (4.3 mm + 0.1") ->  mm

And produces values in both inch and mm, but I want to be able to expand that 
to more units.

I also want to support proper dimensional analysis:

2 mm x 4" -> 203.2 mm^2

While my calculator generally only works with lengths, areas, and angles, I 
figure a general-purpose dimensional analysis library would be useful.

Dimensional analysis has come up before 
(
 and 
).
 It seems support for constant expressions is useful for dimensional analysis, 
and Swift doesn't currently support that.

Given that limitation, what approach would the gurus recommend? The library 
should support:

• Generating a result with derived units based on the input
• Simplifying composite units to some canonical form
• Validating conversion from one (derived) unit to another
• Supporting leniency in conversions (e.g. conflating lb and lb•f).
• Compile-time errors when mixing incompatible types.

In my case, the latter requirement is not so important, since all the 
expressions will be input by the user.

The existing Swift library might be sufficient for my purposes, but I was 
interested in the experts' opinions and suggestions.

Thanks!

-- 
Rick Mann
rm...@latencyzero.com


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