Re: Mathematica 9--Is This A Joke?

• To: mathgroup at smc.vnet.net
• Subject: [mg128861] Re: Mathematica 9--Is This A Joke?
• From: Kevin Wheelock <jiyajbe at gmail.com>
• Date: Sat, 1 Dec 2012 04:32:29 -0500 (EST)
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```Hi David,

As a general rule, I agree with you. However, I don't see that that improves the situation significantly, in this case:

-----------------------------------------------------------------

In[1]:= ClearAll["Global`*"]

In[2]:= eqn1 := F == 1/(4 =CF=80 Subscript[=CE=B5, 0]) (Subscript[q, 1] Subscript[q, 2])/r^2

In[3]:= Solve[eqn1, r]

Out[3]= {{r -> -((Sqrt[Subscript[q, 1]] Sqrt[Subscript[q, 2]])/(
2 Sqrt[=CF=80] Sqrt[F] Sqrt[Subscript[=CE=B5, 0]]))}, {r -> (
Sqrt[Subscript[q, 1]] Sqrt[Subscript[q, 2]])/(
2 Sqrt[=CF=80] Sqrt[F] Sqrt[Subscript[=CE=B5, 0]])}}

In[4]:= r := 1/2 Sqrt[(Subscript[q, 1] Subscript[q, 2])/(=CF=80 F Subscript[=CE=B5, 0])]

(* Now substitute specific values, with their units *)

In[5]:= Subscript[q, 1] := Quantity[1.602*10^-19, "Coulombs"]

In[6]:= Subscript[q, 2] := Quantity[2*1.602*10^-19, "Coulombs"]

In[7]:= F := Quantity[5*10^-6, "Newtons"]

In[8]:= Subscript[=CE=B5, 0] :=
Quantity[8.85*10^-12, "Coulombs^2/(Newtons Meters^2)"]

In[9]:= r

During evaluation of In[9]:= Quantity::unkunit :  "Unable to interpret unit specification  Coulombs^2/(Newtons Meters^2)

-----------------------------------------------------------------

This is NOT an improvement over how version 8 handled this! In ANY way that I can see!

On Nov 30, 2012, at 3:58 AM, djmpark wrote:

> Kevin,
>
> I think the Units package is still there, but just not listed in the
> Standard Extra Packages.
>
> The items that were in PhysicalConstants are now symbols in regular
> Mathematica.
>
> My personal opinion is that it is not very good practice to include units in
> equations at the first step. It is better to keep all the equations strictly
> symbolic, do whatever kind of solving or manipulation you have to do, and
> then at the end substitute values and units to obtain specific answers.
>
>
> David Park
> djmpark at comcast.net
> http://home.comcast.net/~djmpark/index.html
>
>
>
> From: Kevin Wheelock [mailto:jiyajbe at gmail.com]
>
>
> I just installed Mathematica 9. I am horrified. How did this get past QA and
> Usability Testing?
>
> Example: Newton's 2nd Law
>
> In Mathematica 8:
>
> In[1]:= Needs["Units`"]
>
> In[2]:= M := 5 Kilogram
>
> In[3]:= a := 10 Meter/Second^2
>
> In[4]:= F := M a; F
>
> Out[4]= (50 Kilogram Meter)/Second^2
>
> In[5]:= Convert[%, Newton]
>
> Out[5]= 50 Newton
>
>
>
> In Mathematica 9:
>
> In[1]:= M := Quantity[5, "kg"]
>
> In[2]:= a := Quantity[10, "m/s^2"]
>
> In[3]:= F := M a; F
>
> Out[3]= 50kg m/(s)^2
>
> {At this point, Mathematica pops up a dialog offering, among other =
things,
> to let me convert this unit. Okay, I enter "N" in the field I was =
presented}
>
> In[4]:= UnitConvert[
> Quantity[50, ("Kilograms" "Meters")/("Seconds")^2], "N"]
>
> During evaluation of In[4]:= UnitConvert::unkunit: Unable to =
interpret unit
> specification N. >>
>
> Out[4]= UnitConvert[50kg m/(s)^2,N]
>
> {Huh. Okay, I try other things...}
>
> In[5]:= UnitConvert[
> Quantity[50, ("Kilograms" "Meters")/("Seconds")^2], N]
>
> During evaluation of In[5]:= UnitConvert::unkunit: Unable to =
interpret unit
> specification N. >>
>
> Out[5]= UnitConvert[50kg m/(s)^2,N]
>
> In[7]:= UnitConvert[
> Quantity[50, ("Kilograms" "Meters")/("Seconds")^2], "Newton"]
>
> During evaluation of In[7]:= UnitConvert::unkunit: Unable to =
interpret unit
> specification Newton. >>
>
> Out[7]= UnitConvert[50kg m/(s)^2,Newton]
>
> In[8]:= UnitConvert[
> Quantity[50, ("Kilograms" "Meters")/("Seconds")^2], "Newtons"]
>
> Out[8]= 50N
>
> {Ha! I finally guessed right!}
>
> Who the HELL thinks this is better????? "M := Quantity[5,"kg"]"??? =
Are you
> KIDDING ME????
>
> Give me back version 8, and QUICKLY!
>

```

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