covariance

I'm stuck trying to translate some Java code that uses (bounded) wildcard generics to C#. My problem is, Java seems to allow a generic type to be both covariant and contravariant when used with a wildcard. For instance: Java: interface IInterf { } class Impl implements IInterf { } interface IGeneric1<T extends Impl> { void method1(IGeneric2<?> val); void method1WithParam(T val); } interface IGeneric2<T extends Impl> { void method2(IGeneric1<?> val); } abstract class Generic<T extends Impl> implements IGeneric1<T>, IGeneric2<T> { public void method1(IGeneric2<?> val2) { val2.method2(this); } }

This question already has an answer here: Covariance and contravariance real world example 8 answers While reading a section of an article about covariance and contravariance at Wikipedia, I ran into the following, bolded sentence: First consider the array type constructor: from the type Animal we can make the type Animal[] ("array of animals"). Should we treat this as Covariant: a Cat[] is a Animal[] Contravariant: a Animal[] is a Cat[] or neither (invariant)? If we wish to avoid type errors, and the array supports both reading and writing elements, then only the third choice is safe. Clearly

In my attempt to perform cholesky decomposition on a variance-covariance matrix for a 2D array of periodic boundary condition, under certain parameter combinations, I always get LinAlgError: Matrix is not positive definite - Cholesky decomposition cannot be computed . Not sure if it's a numpy.linalg or implementation issue, as the script is straightforward: sigma = 3. U = 4 def FromListToGrid(l_): i = np.floor(l_/U) j = l_ - i*U return np.array((i,j)) Ulist = range(U**2) Cov = [] for l in Ulist: di = np.array([np.abs(FromListToGrid(l)[0]-FromListToGrid(i)[0]) for i, x in enumerate(Ulist)]) di

I read the following paper( http://www3.stat.sinica.edu.tw/statistica/oldpdf/A10n416.pdf ) where they model the variance-covariance matrix Σ as: Σ = diag(S)*R*diag(S) (Equation 1 in the paper) S is the k×1 vector of standard deviations, diag(S) is the diagonal matrix with diagonal elements S, and R is the k×k correlation matrix. How can I implement this using PyMC ? Here is some initial code I wrote: import numpy as np import pandas as pd import pymc as pm k=3 prior_mu=np.ones(k) prior_var=np.eye(k) prior_corr=np.eye(k) prior_cov=prior_var*prior_corr*prior_var post_mu = pm.Normal("returns"

I have the following code. class Header<T> where T: IItem { } class HeaderA : Header<ItemA> { } class HeaderB : Header<ItemB> { } interface IItem { } class ItemA : IItem { } class ItemB : IItem { } Header<IItem> h = new HeaderA(); The last line cannot be compiled. Cannot implicitly convert type 'UserQuery.HeaderA' to 'UserQuery.Header<UserQuery.IItem>' HeaderA is a subtype of Header and ItemA is a subtype of IItem. Why it doesn't work? KeithS In short, you're trying to use a concept called covariance , which is not supported in .NET generic classes , and not supported by default in interfaces

I've been trying to solve a problem. I'm surprised I haven't been able to find anything really useful on the net. I know that from the eigenvalues of the covariance matrix of the ellipse, the major and the minor axis of the ellipse can be computed. As the following: a1 = 2*sqrt(e1) a2 = 2*sqrt(e2) where a1 and a2 are the major and minor axis, e1 and e2 are the eigenvalues of covariance matrix. My question is: given an edge points (xi,yi) of the image ellipse, how it possible to find the 2×2 covariance matrix of that ellipse? Just by pure reverse engineering (I'm not familiar anymore with this

I have a particular class that stores a piece of data, which implements an interface: template<typename T> class MyContainer : public Container<T> { class Something : public IInterface { public: // implement *, ->, and ++ here but how? private: T x; }; // implement begin and end here, but how? private: Something* data; // data holds the array of Somethings so that references to them can be returned from begin() and end() to items in this array so the interface will work, but this makes the problem described below }; And I have an array of Something s. I have the need for Something to implement