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From: pippo on 22 Jan 2010 05:40
I'm (almost) new to mathematica ...
I coped this from some tutorial ...

Needs["VectorAnalysis`"]
r1 = {1, -3, 2}
r2 = {3, 7,-5}
r3 = {4, 1, 6}
r={x,y,z}
ScalarTripleProduct[r-r1,r2-r2,r3-r1]==0

the output i get is:
Out[6]= True

:-(

What am I missing ?

Thank you

From: Sjoerd C. de Vries on 23 Jan 2010 07:30
You made an error while copying: the part which reads r2-r2 should
read r2 - r1

Cheers -- Sjoerd

On Jan 22, 12:40 pm, pippo <marco....(a)email.it> wrote:
> I'm (almost) new to mathematica ...
> I coped this from some tutorial ...
>
> Needs["VectorAnalysis`"]
> r1 = {1, -3, 2}
> r2 = {3, 7,-5}
> r3 = {4, 1, 6}
> r={x,y,z}
> ScalarTripleProduct[r-r1,r2-r2,r3-r1]==0
>
> the output i get is:
> Out[6]= True
>
> :-(
>
> What am I missing ?
>
> Thank you


From: Bill Rowe on 23 Jan 2010 07:31
On 1/22/10 at 5:41 AM, marco.fax(a)email.it (pippo) wrote:

>I'm (almost) new to mathematica ... I coped this from some tutorial

>Needs["VectorAnalysis`"]
>r1 = {1, -3, 2}
>r2 = {3, 7,-5}
>r3 = {4, 1, 6}
>r={x,y,z}
>ScalarTripleProduct[r-r1,r2-r2,r3-r1]==0

>the output i get is: Out[6]= True

>What am I missing ?

What where you expecting? The middle argument given to
ScalarTripleProduct is r2-r2 which is clearly {0,0,0}. If any
one of the three vectors is {0,0,0} the triple scalar produce
will be zero. So, Mathematica has correctly reported the
computed triple scalar product equals 0.


From: Simon on 23 Jan 2010 07:32
On Jan 22, 6:40 pm, pippo <marco....(a)email.it> wrote:
> I'm (almost) new to mathematica ...
> I coped this from some tutorial ...
>
> Needs["VectorAnalysis`"]
> r1 = {1, -3, 2}
> r2 = {3, 7,-5}
> r3 = {4, 1, 6}
> r={x,y,z}
> ScalarTripleProduct[r-r1,r2-r2,r3-r1]==0
>
> the output i get is:
> Out[6]= True
>
> :-(
>
> What am I missing ?
>
> Thank you

I like easy questions... and so does everyone else - I bet you'll get
about 15 replies.
Here's my answer:

r2-r2={0,0,0}

So of course the result will be zero.

Simon

From: Szabolcs Horvát on 23 Jan 2010 07:34
On 2010.01.22. 11:40, pippo wrote:
> I'm (almost) new to mathematica ...
> I coped this from some tutorial ...
>
> Needs["VectorAnalysis`"]
> r1 = {1, -3, 2}
> r2 = {3, 7,-5}
> r3 = {4, 1, 6}
> r={x,y,z}
> ScalarTripleProduct[r-r1,r2-r2,r3-r1]==0
>
> the output i get is:
> Out[6]= True
>
> :-(
>
> What am I missing ?
>

It means that the result of ScalarTripleProduct[r-r1,r2-r2,r3-r1] is 0,
and 0 == 0 is of course True. You have r2-r2 == {0,0,0} in the product
(probably a typo).

Szabolcs

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