1 2 3 4 ... 26 112299 Views 378 Replies Latest reply: May 31, 2011 7:29 AM by A.Non Go to original post
• 632 posts since
May 12, 2010
Currently Being Moderated
15. Oct 11, 2006 3:00 AM (in response to superres)
Working with numbers or variables with Units
Yes, I agree. I use Mathcad largely for physics and electronic engineering problems. I /prefer/ to use units because I think that they contribute to traceability, though I can also see assigning the units in text near the equations. I am also a programmer of many decades, and agree that we can strip the units going into a process that can't handle them. As for restoring them upon return from some process -- well, I think that that might be possible during the assignment of the return variable. But there may be functions - such as solvers - that would be in the position of accepting divers sorts of units on the input, stripping the units, and then not knowing how to apply units upon return. In that case, assigning them after the return is the only recourse. Please understand that I have very little exposure to most of Mathcad compared to many of the collabs.

I also would like to use Maple more often, but it doesn't handle equation entry as nicely as Mathcad, nor do I care at all for its handling of unit.
Rich
http://www.DownEastEngineering.com/
• 15,155 posts since
Nov 15, 2007
Currently Being Moderated
16. Oct 11, 2006 3:00 AM (in response to PhilipOakley)
Working with numbers or variables with Units

1. NO unit system at all

2. a unit system for the natural maths (trig: �, rad, sterad ...)

What you need is :

1. express the independent domain in measured values or graphing unit

2. determine the math dimension of the task for the dependent result.

Example: measured = mV, calculated = �C

Example: B�zier point = graphing unit, arc length = graphing unit.

Units in solvers ? !

For your Odesolve, no problem. Generally as the time runs Cartesian X the response is Y displacement vs time .

jmG
Attachments:
• 632 posts since
May 12, 2010
Currently Being Moderated
17. Oct 11, 2006 3:00 AM (in response to PhilipOakley)
Working with numbers or variables with Units
Sorry - http reference no longer available...?

Rich
http://www.DownEastEngineering.com/
• 4,704 posts since
Jun 1, 2007
Currently Being Moderated
18. Oct 11, 2006 3:00 AM (in response to superres)
Working with numbers or variables with Units
On 10/11/2006 11:57:39 AM, eden_mei wrote:
== That's where Mathcad can cut to the chase. You don't need Uconeer or another units converter with Mathcad. The ideal gas equation will work with any combination of units from the different choices transparently.
== You seem to want to go out of your way to complicate your life with a separate units conversion when Mathcad does the unit conversion transparently and without having to transfer numbers from one program to another.

Agreed. I'm not a units user, but there would seem to be little point in using A N Other product merely to do unit conversions on calculations otherwise done in Mathcad, and then copy/paste them.

It also introduces yet another configuration problem when (the almost inevitable) changes are made to a worksheet or the user wants different values.

If Mathcad is short of a particular unit (expressible in terms of the base quantities), then it's not too difficult to add that unit.

AFAICT, the major problem with using units in Mathcad is not the basic functionality, but some of the difficulties that occur in the flow of information through a document, for example, the need to remove/add units for certain operations, and the lack of mixed units in arrays.

Stuart
• 15,155 posts since
Nov 15, 2007
Currently Being Moderated
19. Oct 11, 2006 3:00 AM (in response to ptc-1368288)
Working with numbers or variables with Units
... nearly all (if not) the collabs with units were and are still in the disciplines of "Structural", "Civil Engineering" ... Maybe because those Engineering disciplines don't really involve non geometrical Units ?

jmG
• 15,155 posts since
Nov 15, 2007
Currently Being Moderated
20. Oct 11, 2006 3:00 AM (in response to ptc-1368288)
Working with numbers or variables with Units
To convince yourself that units are useless and that you should use work done by others before you , try that one:

P*V := Z*n*R*T

with 14 pressure bases, 10 volume bases, 3 mole bases, 2 temperature bases

jmG
• 7,759 posts since
Jun 1, 2007
Currently Being Moderated
21. Oct 11, 2006 3:00 AM (in response to StuartBruff)
Working with numbers or variables with Units
Luckily, I don't have many of those situations.

I would expect, though, that stripping and reinserting units can be made automatic once the calculation is set up and it can, again, be transparent at the input side of thing.

TTFN,
Eden
• 15,155 posts since
Nov 15, 2007
Currently Being Moderated
22. Oct 11, 2006 3:00 AM (in response to FredKohlhepp)
Working with numbers or variables with Units
"Uconeer" is for those who don't have Mathcad at the end level, for instance Technicians plugging things in a Control system.
Among the so many converters Uconeer is quite complete vis the inconsistency in units used in real life as many users must stick to an original system for consistency ... a coal fired power plant designed in 1958 (steam properties and so and so ...).

Few more pages complete the work sheet (not included) with a solver . No need to preach including units in this kind of task . The formula is designed+dimensioned, just enter the correct values (converted if required).

The formula comes out from the Toricelli principle, yes it takes a bit of caution to make it work . You are right, at the design stage Mathcad with units would have helped but not anymore . The same principle applies to all engineering formulas developed without Mathcad . That's why I maintain that units in Mathcad are useless, at least most collabs can survive without units in Mathcad . Units were added to help the beginners, but not added to be used .

jmG
Attachments:
• 4,704 posts since
Jun 1, 2007
Currently Being Moderated
23. Oct 12, 2006 3:00 AM (in response to StuartBruff)
Working with numbers or variables with Units
On 10/12/2006 2:07:08 AM, stuartafbruff wrote:
> http://www.apa.org/journals/features/psp7761121.pdf

I think Dilbert has been making the point for several years.

Stuart

• 4,704 posts since
Jun 1, 2007
Currently Being Moderated
24. Oct 12, 2006 3:00 AM (in response to Ninetrees)
Working with numbers or variables with Units
On 10/11/2006 7:13:53 PM, woodwise wrote:
== Sorry - http reference no longer available...?

http reference available...?

http://www.apa.org/journals/features/psp7761121.pdf

Stuart
• 7,759 posts since
Jun 1, 2007
Currently Being Moderated
25. Oct 12, 2006 3:00 AM (in response to ptc-1368288)
Working with numbers or variables with Units
In an ideal world, everyone will be using a single unified set of units.

The reality is that a customer will specify a 3 inch ground sample distance at 1804 meter distance. It would be absolutely asinine to not use Mathcad's built-in conversion to get the required microradians of resolution. The calculation is simple, and straightforward and does not require any additional explanation or clarification of a separate and manual unit conversion

GSD:3in
Dist:1804m
IFOV:GSD/Dist

TTFN,
Eden
• 101 posts since
Dec 11, 2008
Currently Being Moderated
26. Oct 13, 2006 3:00 AM (in response to ptc-1368288)
Working with numbers or variables with Units
On 10/11/2006 4:01:27 PM, jmG wrote:
>... nearly all (if not) the
>collabs with units were and
>are still in the disciplines
>of "Structural", "Civil
>Engineering" ... Maybe because
>those Engineering disciplines
>don't really involve non
>geometrical Units ?
>
>jmG

Maybe because those disciplines, plus physics, etc are connected to the real world where we measure things with micrometers, balances, etc. And what do you mean by non-geometrical units?

If you don't need to use units in your discipline then that's fine -- no-one will tell you to. But the work a lot of us do has to use units or it is completely meaningless. If I tried to figure out what resolution I could get on the sky with an array of antennas of size 10 with a spacing of 2 and a wavelength of 3, I couldn't do it! It is only with units that it makes sense and Mathcad does that for me exactly the way I want.

I can even do the Hankel transforms with units in the integral limits and work out the beam pattern in arcminutes -- trivially. Why would I not?

-James
• 15,155 posts since
Nov 15, 2007
Currently Being Moderated
27. Oct 14, 2006 3:00 AM (in response to lamb)
Working with numbers or variables with Units
... suite of :

� you advocate you can't do your job without units, then, could you or the could your profession do the job in DOS or else compiled languages that don't take units . Could you do the job in TI =59, HP-48SX ... ?

Hankel or else functions only relate the dependent domain to the independent one. Do you have to put units in mhyper(2.5,1,x) ?

I see no units in the attached Galerkin finite differences. However some collab suggested Odesolve should carry unit.

The PID Optimize (attached) starts with units and properties but by the "Harry magic" the final answer are coefficients apparently unitless but they are not as they are in "repeat per minute" .

I'm short of time to look at your antenna sheet, other collabs might find useful.

jmG

• 15,155 posts since
Nov 15, 2007
Currently Being Moderated
28. Oct 14, 2006 3:00 AM (in response to ptc-1368288)
Working with numbers or variables with Units

Yours is in your hart, mine has evaporated .

jmG
Attachments:
• 15,155 posts since
Nov 15, 2007
Currently Being Moderated
29. Oct 15, 2006 3:00 AM (in response to StuartBruff)
Working with numbers or variables with Units
Stuart,

Did you have a point here ?

Why don't you open the last little sheet "UnitOf_Graphing_NURBS"

To resume :

assign the values to vars, use native formulas done by knowledgeable persons and append the corresponding "Unit result" . That way get rid of units in Mathcad . Any QA team will check on a independent unitless calculator . Convert beforehand not after .

jmG
1 2 3 4 ... 26

#### More Like This

• Retrieving data ...