Re: Engineering requests

• To: mathgroup at smc.vnet.net
• Subject: [mg125303] Re: Engineering requests
• From: "McHale, Paul" <Paul.McHale at excelitas.com>
• Date: Mon, 5 Mar 2012 02:41:56 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <jiqflj\$3o\$1@smc.vnet.net> <201203031152.GAA14440@smc.vnet.net>

```Daniel,

Thanks for the ideas.  The minimalUnits[] is interesting.  It would be very interesting to assign variables values with units.  Likely, another data type would be required to support this.
R1= 5 Ohm;

I tried to use interval.  Maybe I'm not doing it right...

R1int={100000-100000*(0.1),100000+100000(0.1)}
R2int={30000-30000*(0.1),30000+30000(0.1)}

(* Using interval (wrong answers) *)
R1=Interval[R1int];
R2=Interval[R2int];
Vout=5/(R1+R2) R2 // Max
Vout=5/(R1+R2) R2 // Min

Out[1]= 1.41026
Out[2]= 0.944056

(* using table   (correct answers)    *)
R1=R1int;
R2=R2int;
Table[5/(Ra+Rb) Rb,{Ra,R1},{Rb,R2}]// Max
Table[5/(Ra+Rb) Rb,{Ra,R1},{Rb,R2}]// Min

Out[3]= 1.34146
Out[4]= 0.985401

Table[] is actually getting me by.  The dimensional analysis would be very interesting, but again, we (I) get by without it.  The other engineers use dimensional analysis available in the other software.  It should be noted, it is quite limited in the other software.  Direct evaluation of relatively simple algebraic formula is supported, but it is clearly not supported by many functions.

I have a mListFFT[] I've written.  I will post it in another thread for comments.  It is limited.  But works well enough for simple viewing of spectral content.

Paul

Paul McHale  |  Electrical Engineer, Energetics Systems  |  Excelitas Technologies Corp.

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Thank you

-----Original Message-----
From: danl at wolfram.com [mailto:danl at wolfram.com]
Sent: Saturday, March 03, 2012 6:53 AM
To: mathgroup at smc.vnet.net
Subject: [mg125303] Re: Engineering requests

On Friday, March 2, 2012 6:49:55 AM UTC-6, McHale, Paul wrote:
> So, here are some problems we face, but don't have great answers for in Mathematica.
>
> 1. Dimensional analysis.  To do this, we must have unit support.  The best description of this is the ability to calculate (V/R)^2 R and have it return a unit of watts.  Other programs handily support this (though they are sorely lacking in other places :))

Probably not exactly what you want, but you might have a look here.

http://library.wolfram.com/infocenter/Conferences/7513/

In[40]:= minimalUnits[(v/o)^2*o]
Out[40]= {Watts}

> 2. Tolerances support.  One difficulty we have is determining the min/max at a certain point in a circuit even if the circuit is not complicated to model.  I use lists {Rmax,Rmin} and Table.  Works, but is a little clumsy.
> [...]

Have you tried using Interval[...] to specify value ranges? For basic arithmetic this should offer some possibilities. If you are computing, say, solutions to differential equations with toleranced input values, that will be more of a challenge. In effect what one wants is some sensitivity analysis.  Can be done (using NDSolve), but is not so simple. That is to say, I do not recall the details of the setup.

Daniel Lichtblau
Wolfram Research

```

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