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# Simplex Method Help

Maths and statistics discussion, revision, exam and homework help.

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1. Simplex Method Help
This may be quite difficult to describe, but I'll try my best...

Consider a simplex tableu, where you're currently trying to find the pivot point, after having found out your pivot column.

From here we understand we must divide our Right Hand Side (RHS) column by our values in the corresponding pivot column. Now suppose one of our numbers in the RHS column was 0, if we were to divide this number by its corresponding pivot column number, we would automatically be able to deduce that this is equal to 0. Since this is 0, our obvious lowest number, do we take that number corresponding to it in the pivot column as our pivot point?

The reason I ask is because I attempted a question on OCR Decision 1 Misc 8 Exercise 2, and when I was faced with this situation, I assumed it was in fact the pivot point, but ended up with an incorrect answer, so I'm concerned as to whether this is a general rule with the Simplex method or I'm just making silly mistakes. Since the only rules I'm aware of when considering the pivot row are...

1. You ignore dividing the RHS by the corresponding pivot column if the RHS value is negative

2. You ignore dividing the RHS by the corresponding pivot column if the pivot column value is 0 (since this will give infinity)

Thank you very much, much help would be appreciated :-)
Last edited by BobGreggary; 05-05-2012 at 00:59.
2. Re: Simplex Method Help
I read that although when you divide zero by a positive or a negative number the result is numerically zero, you have to treat the ratio 0/negative as negative which may exclude it from consideration...
3. Re: Simplex Method Help
(Original post by BobGreggary)
This may be quite difficult to describe, but I'll try my best...

Consider a simplex tableu, where you're currently trying to find the pivot point, after having found out your pivot column.

From here we understand we must divide our Right Hand Side (RHS) column by our values in the corresponding pivot column. Now suppose one of our numbers in the RHS column was 0, if we were to divide this number by its corresponding pivot column number, we would automatically be able to deduce that this is equal to 0. Since this is 0, our obvious lowest number, do we take that number corresponding to it in the pivot column as our pivot point?

The reason I ask is because I attempted a question on OCR Decision 1 Misc 8 Exercise 2, and when I was faced with this situation, I assumed it was in fact the pivot point, but ended up with an incorrect answer, so I'm concerned as to whether this is a general rule with the Simplex method or I'm just making silly mistakes. Since the only rules I'm aware of when considering the pivot row are...

1. You ignore dividing the RHS by the corresponding pivot column if the RHS value is negative

2. You ignore dividing the RHS by the corresponding pivot column if the pivot column value is 0 (since this will give infinity)

Thank you very much, much help would be appreciated :-)

the reference is http://math.uww.edu/~mcfarlat/simplex1.htm

go to "step 5"

4. Re: Simplex Method Help
(Original post by the bear)
the reference is http://math.uww.edu/~mcfarlat/simplex1.htm

go to "step 5"

Thank you so much! :-)
5. Re: Simplex Method Help
(Original post by BobGreggary)
Thank you so much! :-)
Glad to be of help... i have always been a bit nervous of the Simplex method

[ don't think the name is at all appropriate !! ]
6. Re: Simplex Method Help
(Original post by the bear)
Glad to be of help... i have always been a bit nervous of the Simplex method

[ don't think the name is at all appropriate !! ]
Yer haha, totally agree!

7. Re: Simplex Method Help
OMFG I completely hate this!!! I was cruising through D1 until I hit a stop. This bloody Simplex method! Load of gibberish about pivot rows! And I never know when it's a minus or a plus when you combine all that's freaking going on!!!

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Last updated: July 2, 2012
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