Recent content by patata

Hi all, Probably a stupid question, but in general, is it true that Var[x] + Var[Y] -2Cov(X,Y) > 0? I'm having trouble figuring out why a number of articles I seem to have read take this for granted without demonstrating why (which makes me think it could be fairly trivial...). Thanks for...

Homework Statement Let S be the set of all functions u: N -> {0,1,2} Describe a set of countable functions from S Homework Equations We're given that v1(n) = 1, if n = 1 and 2, if n =/= 1 The function above is piecewise, except i fail with latex The Attempt at a Solution...

As some attempted working, If i multiply A(A^-1 +2B^-1)2B does that give me I? Essentially what I am finding most confusing is how to deal with the terms in the brackets.

Homework Statement Let A,B and and 2A + B be invertible n x n matrices. Show that (A^-1 + 2B^-1) is also invertible and express (A^-1 + 2B^-1)^-1 in terms of A, B and (2A+B)^-1 The Attempt at a Solution I'm not exactly sure how to tackle this problem, i know that for a matrix to be...

Thanks for your help Halls, your reasoning makes sense, however, the next non-dimensionalised variable we have to introduce is y = a / amax, so wouldn't this also represent the fraction of the maximum age the animal has lived? keeping in mind that 'a' is the age of the organism.. Thanks...

Hi there everybody, while not a specific homework problem, in my PDE class i have come along a question which i don't quite understand. Now, when non-dimensionalising an equation, i believe the purpose is to remove the units from it? Now, we are talking about a biological population and are...

Thank you for the quick and speedy reply! I understand the case for x^2y but i made a typo and the example for the book is x^3y... If i convert this to polar coordinates i get r^3Cos^3(theta) x rSin(theta) / r^2 (Cos^2(theta)Sin^2(theta) However, i am getting stuck here, are there any ways...

Like many people on this forum, i am seemingly having a lot of trouble grasping the concepts of Epsilon Delta proofs and the logic behind them. I have read the definition and i realize for e>0 there is a d>0 such that... 0<sqrt((x-1)^2 - (y-b)^2) < d then f(x,y) - L <e (excuse my use of...

Thanks for the help guys but I am still getting something wrong, which I am guessing is a small but stupid mistake... for df/dx i get 1/(1+x) . -1(log(1+y))^-2 (unless that's right?) for df/dy I am confused...whats the derivative of a log of a constant :S Thanks for any help =)

Hey everybody, first time poster although I've recently come across this forum and it's helped me discover the solution of many problems I've been having. I've seen to come to grips with most partial derivative problems I've come across, however, i still can't get correct solutions to problems...