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From: Maria Davis on 7 Mar 2010 05:14
Hi;
I have such equations:
x=a+b
y=c+d
a=z+t
b=y

I want to use mathematica in order to simplify x and obtain: x=z+t+c
+d
I have used: [x,Listofequations]
This function is available if I have equations written in the
following order:
x=a+b
a=z+t
b=y
y=c+d

but in the case of non ordered equations, it doesn't work. Further, I
must use equations in the order given.
Please can you help me.
Thanks

From: Sjoerd C. de Vries on 8 Mar 2010 06:12
It's not particularly clear what your problem is but can't you use Set
Dealyed (:=) ?

x := a + b
y := c + d
a := z + t
b := y
x

c + d + t + z

Cheers -- Sjoerd

On Mar 7, 12:14 pm, Maria Davis <arbi...(a)gmail.com> wrote:
> Hi;
> I have such equations:
> x=a+b
> y=c+d
> a=z+t
> b=y
>
> I want to use mathematica in order to simplify x and obtain: x=z+t+c
> +d
> I have used: [x,Listofequations]
> This function is available if I have equations written in the
> following order:
> x=a+b
> a=z+t
> b=y
> y=c+d
>
> but in the case of non ordered equations, it doesn't work. Further, I
> must use equations in the order given.
> Please can you help me.
> Thanks


From: Bill Rowe on 8 Mar 2010 06:14
On 3/7/10 at 5:10 AM, arbiadr(a)gmail.com (Maria Davis) wrote:

>I have such equations:
>x=a+b
>y=c+d
>a=z+t
>b=y

In Mathematica, these are assignments, not equations. An
equation is written using "==" not "=" in Mathematica.

>I want to use mathematica in order to simplify x and obtain:
>x=z+t+c +d I have used: [x,Listofequations] This function is
>available if I have equations written in the following order: x=a+b
>a=z+t b=y y=c+d

It is hard to comment on the above since you omitted the
function you tried. In any case, first create a list of equations

In[1]:= eqns = {x == a + b, y == c + d, a == z + t, b ==
= y};

then the desired result can be obtained using Eliminate as follows:

In[2]:= Eliminate[eqns, {a, b, y}]

Out[2]= c+d+t+z==x


From: Bob Hanlon on 8 Mar 2010 06:18
eqns = {x == a + b, y == c + d, a == z + t, b == y};

x == (x //. Rule @@@ eqns)

x == c + d + t + z

This works for any ordering of the equations

Union[x == (x //. Rule @@@ #) & /@ Permutations[eqns]]

{x == c + d + t + z}


Bob Hanlon

---- Maria Davis <arbiadr(a)gmail.com> wrote:

=============
Hi;
I have such equations:
x=a+b
y=c+d
a=z+t
b=y

I want to use mathematica in order to simplify x and obtain: x=z+t+c
+d
I have used: [x,Listofequations]
This function is available if I have equations written in the
following order:
x=a+b
a=z+t
b=y
y=c+d

but in the case of non ordered equations, it doesn't work. Further, I
must use equations in the order given.
Please can you help me.
Thanks


From: dh on 9 Mar 2010 06:18
Hi,
ReplaceRepeated (not ReplaceAll) can do the job:
a + b //. {y -> c + d, a -> z + t, b -> y}
Daniel

On 07.03.2010 11:14, Maria Davis wrote:
> Hi;
> I have such equations:
> x=a+b
> y=c+d
> a=z+t
> b=y
>
> I want to use mathematica in order to simplify x and obtain: x=z+t+c
> +d
> I have used: [x,Listofequations]
> This function is available if I have equations written in the
> following order:
> x=a+b
> a=z+t
> b=y
> y=c+d
>
> but in the case of non ordered equations, it doesn't work. Further, I
> must use equations in the order given.
> Please can you help me.
> Thanks
>


--

Daniel Huber
Metrohm Ltd.
Oberdorfstr. 68
CH-9100 Herisau
Tel. +41 71 353 8585, Fax +41 71 353 8907
E-Mail:<mailto:dh(a)metrohm.com>
Internet:<http://www.metrohm.com>


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