User talk:Johngcarlsson

Welcome!

Hello, Johngcarlsson, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are some pages that you might find helpful:

I hope you enjoy editing here and being a Wikipedian! Please sign your name on talk pages using four tildes (~~~~); this will automatically produce your name and the date. If you need help, check out Wikipedia:Questions, ask me on my talk page, or place {{helpme}} on your talk page and ask your question there. Again, welcome!

And a few style notes. One is that one should use lower case in section names, so

 ==Standard form==

instead of

 ==Standard Form==

and second that using an edit summary is helpful for others reviewing your work. Enjoy the wiki. – Oleg Alexandrov (talk) 16:06, 15 February 2007 (UTC)[reply]

Many optimization problems are hard to solve[edit]

Hi John. Also a warm welcome from me. I have been enjoying your efforts to get our optimization articles in better shape. However, I'm a bit unsure about your latest change to Optimization (mathematics). You say that there are several classes of optimization problems, like LP, and that most classes are hard, but convex is not. I'm a bit worried that the way you formulate and combine these statements leads the reader to conclude that linear programming must be hard and thus not convex optimization. I'm having problems formulating quite what my issue is, so perhaps I'm just chasing some fleeting illusion, but could you please have another look at the paragraph you added?

By the way, have you already found Wikipedia:WikiProject Mathematics, the meeting place for people interested in working on the maths articles? We have a list of participants; feel free to introduce yourself there. The associated talk page is a good place if you want to contact mathematicians.

I hope that you are enjoying yourself here and that I will see more of your contributions soon! Cheers, Jitse Niesen (talk) 11:37, 1 March 2007 (UTC)[reply]

Quasiconvex function[edit]

Hi. Why do you think it is false for a quasiconvex function that

Any local minimum is a global minimum.

You can reply here, thanks. Oleg Alexandrov (talk) 16:04, 1 March 2007 (UTC)[reply]

Hi Oleg, consider the function

f(x) = |x| for x < 1

f(x) = 1 for x >= 1

This has a local minimumn wherever x>= 1, but it's not a global minimum.Johngcarlsson 20:16, 1 March 2007 (UTC)[reply]

You are right. To my credit, it was not me who added in that statement, but I was nevertheless sure it was true. Thanks. Oleg Alexandrov (talk) 04:35, 2 March 2007 (UTC)[reply]

License tagging for Image:Ellipsoid 1.png[edit]

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Edit summary[edit]

Hi. It would be nice if you could use an edit summary explaining your changes. Thanks for your work, particularly the new Subgradient method article. Oleg Alexandrov (talk) 03:14, 7 March 2007 (UTC)[reply]

Linear matrix inequality[edit]

After this edit of yours to linear matrix inequality, the article says that "the $A\leq 0$ inequality means that A is a negative-definite matrix". I assume that you mean negative semi-definite? If so, could you please fix that? If not, sorry for bothering you. Cheers, Jitse Niesen (talk) 06:12, 15 March 2007 (UTC)[reply]

Re:Posynomial[edit]

I replied on my talk page. Oleg Alexandrov (talk) 15:03, 5 April 2007 (UTC)[reply]

File permission problem with File:Ellipsoid 1.png[edit]

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File permission problem with File:Ellipsoid 2.png[edit]

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File permission problem with File:Ellipsoid 3.png[edit]

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File permission problem with File:Ellipsoid 4.png[edit]

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File permission problem with File:Ellipsoid 5.png[edit]

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File permission problem with File:Ellipsoid 6.png[edit]

Thanks for uploading File:Ellipsoid 6.png. I noticed that while you provided a valid copyright licensing tag, there is no proof that the creator of the file has agreed to release it under the given license.

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