User talk:Mark viking

Restriction (mathematics)

Hello! I agreed with your assessment of restriction (mathematics) as a stub, and so I've been trying to get it to at least a somewhat usable level. I'd like to get it to a C level. In your opinion, what more does it need before it reaches that point? Thanks, Brirush (talk) 19:01, 10 October 2014 (UTC)

Hi Brirush! You have already done a good job organizing the article, expanding it and adding references--beyond start and heading to C. This is sort of a limited subject, so I don't think much more would be needed for C class. A few ideas:

• Indicate what a restriction is good for. The plot in the article demonstrates a main use: cut out the undefined/singular bits of a function to make it well behaved. In topology, the neighborhood is sometimes used as a kind of restriction. In database theory or relational algebra, a restriction in the form of a selection operator is a fundamental operation, useful for filtering and for specifying joins.
• How do restrictions relate to other similar concepts? Clarify the difference between projection and restriction, for instance--one is a subset, the other a map to a new space. How are restriction and corestriction related?
• Notation: some people use ${f|}_{A}$ and some people use $f{\upharpoonright _{A}}$. We should probably note both notations.

I attempted to expand and clarify the definition, please check that I didn't introduce errors or infelicities. Please take or leave these suggestions according to your good taste. Thanks, --Mark viking (talk) 21:10, 11 October 2014 (UTC)

There is also restriction of the range of a function. (Already mentioned.) How this works out in the smooth manifold case can be found in John M. Lee's book Introduction to Smooth Manifolds pp. 190 - 195. Restriction of tensor fields to submanifolds might be worth mention too. Willard's book General Topology lists (as problems to work out) a couple of nontrivial propositions that involve restrictions of functions. One of them is a generalization of the pasting lemma.

Wikipedia's rating policy is rather unrewarding to writers of short, concise and good articles. Ratings often measure length/importance of topic rater than quality. One screen articles almost never get past "Start". YohanN7 (talk) 22:18, 11 October 2014 (UTC)

Seven states of randomness

See if the article is easier to understand now. Perhaps latter I will add a more technical explanation of what Mandelbrot had in mind.Lbertolotti (talk) 00:21, 14 October 2014 (UTC)

Hi Lbertolotti - I think you have done a good job of giving the context of financial risk analysis and management for the seven states of randomness, to help establish why these ideas are important. But I'm not sure if the definition of a quant or its relation to a financial engineer is directly relevant to the subject, other than to say that these are the sorts of people who think about types randomness in their models. Regards, --Mark viking (talk) 03:13, 14 October 2014 (UTC)

Well, risk management has been done for a long time without using math. Financial engineer practice is what is directly affected by Mandelbrot's work.Lbertolotti (talk) 13:10, 14 October 2014 (UTC)

Diastolic higher than sistolic

Hello Mark, You answer me on reference desk "This can happen when Intra-aortic balloon pumps are used, but that is a specialized case of an external pump out of phase with the heart." Can you explain me why in this case it can be- please? I thank you deeply213.57.99.239 (talk) 16:22, 23 November 2014 (UTC)