Recent content by AndreTheGiant

I have a similar problem, so then in this one the hessian should be used for the Volume function in terms of l and w or 2 variables instead of all 3?

Homework Statement I have been given a 4x4 hessian matrix at a point c. I want to find out if the point is a local min/max/saddle. I am aware of the conditions of critical points for 3x3 hessians, but I'm not sure about 4x4 hessians. The hessian is given by 1 0 -2 1 0 2 0 -1 -2 0 5 2 1 -1 2...

Ah ok. I think i got it. In the hessian which is given by fxx fxy fyx fyy fxy is not equal to fyx which should be the case for mixed partials?

Homework Statement Given a function f: R^2 -> R of class C^3 with a critical point c. Why CANNOT the hessian matrix of f at point c be given by: 1 -2 2 3 Homework Equations The Attempt at a Solution So first i want to clarify this. When it says f: R^2 -> R, that...

When i have stuff like E(E(X)) or E(E(XY|X)) etc how do i evaluate a double expectation? and for random vectors stuff like E(E(X)'Y) or E(X'E(Y)) etc.

This is a one way Anova problem. Ancova isn't covered just yet. Its a regression analysis course. I have my notes but I am still confused and i can't find anything about this on the web really that explains it in the same notation or way my instructor does. I'm really trying to understand it.

It is a homework question and about your points. The first one is correct that is what i meant. The second one is also correct, i forgot to put the subscript n on the k. As for the first part. I also made a mistake there. It asks to write down E(Y|T) in terms of X1...Xi dummy variables, not Y...

Hi there. I am having some trouble understanding the full context of this question. Suppose we have a categorical variable T E (1...n) and we observe k observations for Y when T = n. If a regression model holds: i) Write down Y in terms of dummy variables X1...Xi ii) What is the...

Homework Statement I am having lots of trouble understanding how to get the kernel of linear transformations. I get that you basically set it equal to zero and solve. T: P3 → P2 given by T(p(x)) = p΄΄(x) + p΄(x) + p(0) Find ker(T) The Attempt at a Solution So P3 = ax^3 + bx^2 +...

Thanks! That cleared up so much... Another quick question if you may know. If i have the observations. (xi1,...xik,yi1,...,yim). If i set X = (xij) and Y = (yij). What are those? Is that an i x k matrix for X and an i x m matrix for Y?

Homework Statement So yeah as the topic says. What does R^(nxm) mean? Is that a matrix or an n x m space. The notation is really confusing and sometimes it means something else. I'm doing regression analysis right now and this shows up a lot. Is it a matrix when you say something like C =...

Hi thanks for the replies. I'm still a bit lost on this. I tried the method suggested by tjackson. Basically if r is the distance from p to x,y,z and from q to x,y,z then they should be equal. Makes sense. However how do i even get this equation without knowing the points p and q? the distance...

Homework Statement Show that the points in R3 equidistant from two fixed points, p and q, form a plane and find the equation of the plane. Homework Equations The Attempt at a Solution So the equation of the plane takes the form ax + by+ cz = d, where (a,b,c) is a normal vector...

cx^2 + cy - x + y^2 = 0 so when c = 0 i get a parabola, but what about when c = 2 for example..?

...right! stupid mistakes :( thanks so much for the help!