I was about to be late for my condensed matter physics class, and suddenly the chain on my bike dropped. I cannot have worse luck today.
follow me on Mastodon
By recursively integrating according to from , we can get the solution of the ODE with initial conditions as the limit of the sequence of functions.
To illustrate the concept about non-uniform elements, we study a simple problem: suppose a uniform heavy elastic rope has mass , original length , and stiffness , and find the mass distribution and length of it when hung vertically. We can use the element method to solve this problem, but the elements are non-uniform in terms of length. The elements add up to get the total length .
In this article, we will find that the inertia matrix naturally appears when we calculate the kinetic energy or the angular momentum of a rigid body. Then, we introduce the concept of principal inertia . We also study how the inertia matrix changes under translations and rotations and how those transformations may lead to conclusions that can help us simplify the calculation of inertia matrices.
The Hölder mean of with weights and a parameter is defined as , and the value at are defined by the limits. We can prove using Jensen’s inquality that the Hölder mean increases as increases. This property can be used to prove HM-GM-AM-QM inequalities.
The function is a polynomial of degree w.r.t. , and the sum of its coefficients is . This turns out to be properties of Eulerian numbers.
The image of a circle with radius and centered at through a thin lens at with focal length and centered at is a conic section with the focus being , the directrix being line , and the eccentricity being .
Suppose is a point on the circle . When is the sum of distances from to two edges of extremal? It turns out to be related to angle bisectors (the intersections of and the bisector of or its adjacent supplementary angle are extremals), while the edge cases (at the intersections of and edges of ) are a little tricky: we need to use the bisectors to divide the plane into four quadrants, pick the two quadrants where the line intersecting at lies, translate the region to make it center at , and see whether is inside the translated region.
After some comparison among solutions, I use KaTeX to typeset math in my emails.
There is a canonical transform of the Kepler problem which is the same as the problem of motion of a free particle on 3-sphere. The explicit formula of the transform as well as some links about this topic is written in the article. The explicit formula for is where is the position of the particle on 3-sphere (a 4-dimensional vector), is the momentum of the original particle in Kepler problem, is a vector perpendicular to the 3-dimensional hyperplane where lies, and .
By using power series, we can prove that the problem of solving linear homogeneous ODE with constant coefficients can be reduced to the problem of solving a polynomial with those coefficients. This article illustrates this point in detail, but it uses a very awful notation…
subscribe via RSS