Re: Multiple Constants

• To: mathgroup at smc.vnet.net
• Subject: [mg83264] Re: [mg83215] Multiple Constants
• From: DrMajorBob <drmajorbob at bigfoot.com>
• Date: Fri, 16 Nov 2007 05:33:54 -0500 (EST)
• References: <20087331.1195162053751.JavaMail.root@m35>

```First, you misspelled Constant.

Second, as Help will tell you, the syntax is

SetAttributes[{a, b, c}, Constant]

Third, that only affects Dt, as Help also explains... and you're not using

Dt.

Fourth, these are NOT equations or any other legal syntax in Mathematica,
since "=" means Set, not Equal.

> x+y+z=1
> b*x+c*y+d*z=A
> f*x+g*y+h*z=Q

You mean

eqns = {x + y + z == 1, b x + c y + d z == a, f x + g y + h z == q}

Fifth, b,c,d,A,f,g,h,Q are NOT constants; they're parameters.

Sixth, these are the variables you don't consider "constant":

Complement[
eqns /. Equal -> List // Flatten // Variables, {b, c, d, a, f, g, h,
q}]

{x, y, z}

And finally, here's how you solve for them:

Solve[eqns, {x, y, z}]

{{x -> -((a g - d g - a h + c h - c q + d q)/(
c f - d f - b g + d g + b h - c h)),
y -> -((a f - d f - a h + b h - b q + d q)/(-c f + d f + b g - d g -
b h + c h)),
z -> -((a f - c f - a g + b g - b q + c q)/(
c f - d f - b g + d g + b h - c h))}}

SetAttributes didn't help (or hurt).

Bobby

On Thu, 15 Nov 2007 04:37:30 -0600, <thehammerster at gmail.com> wrote:

> Hi,
> I'm new to Mathematica and I feel like this is a stupid question but I
> can't seem to define more than one constant
>
> If I type
> SetAttributes[a,b,c,Contstant]
> I get
> SetAttributes::argrx: SetAttributes called with 4 arguments; 2
> arguments are \expected.
>
> I have three equations and three variables I want to solve for and I
> have 8 constants.
>
> x+y+z=1
> b*x+c*y+d*z=A
> f*x+g*y+h*z=Q
>
> b,c,d,A,f,g,h,Q are constants and I want a generic equations that I
> can use for many different variations of these constants.
>
> I've done the calculation by hand but fear I have made a mistake and
> would like to double check my calculation, and then use the equation
> to propagate my errors, as each constant has an associated standard
> error of the mean. Propagation of my error will give me an error on my=

> model calculation, which is really important.
>
> Thanks
>
>

-- =

DrMajorBob at bigfoot.com

```

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