What is covariance and Contravariance in physics?

In multilinear algebra and tensor analysis, covariance and contravariance describe how the quantitative description of certain geometric or physical entities changes with a change of basis. In physics, a basis is sometimes thought of as a set of reference axes.

What is covariance and Contravariance in programming?

Covariance means that a method can return a type that is derived from the delegate’s return type. Contra-variance means that a method can take a parameter that is a base of the delegate’s parameter type.

How do you read contravariance and covariance?

Covariance and Contravariance in Delegates

Covariance permits a method to have a return type that is a subtype of the one defined in the delegate.
Contravariance permits a method to have a parameter type that is a base type of the one defined in the delegate type.

What is covariance and Contravariance in generics in Java?

Covariance can be translated as “different in the same direction,” or with-different, whereas contravariance means “different in the opposite direction,” or against-different. Covariant and contravariant types are not the same, but there is a correlation between them.

What is the covariance formula?

In statistics, the covariance formula helps to assess the relationship between two variables. It is essentially a measure of the variance between two variables. The covariance formula is expressed as, Covariance formula for population: Cov(X,Y)=∑(Xi−¯¯¯¯X)(Yi−¯¯¯¯Y)n C o v ( X , Y ) = ∑ ( X i − X ¯ ) ( Y i − Y ¯ ) n.

What are Covectors used for?

MEANING, USAGE & APPLICATIONS: Covectors are the essential structure for differential forms in differential topology/geometry and most of the important developments in those fields are formulated or use them in one way or another.

How is covariance calculated?

Covariance measures the total variation of two random variables from their expected values.
Obtain the data.
Calculate the mean (average) prices for each asset.
For each security, find the difference between each value and mean price.
Multiply the results obtained in the previous step.

What is covariance in Kotlin?

A covariance class is a generic class where subtyping is preserved. In Kotlin, to declare the class to be contravariant on a certain type parameter, you put the in keyword before the name of the type parameter to consume the element type.

What is covariance in Scala?

Covariance allows assigning an instance to a variable whose type is one of the instance’s generic type; i.e. supertype. Contravariance allows assigning an instance to a variable whose type is one of the instance’s derived type; i.e. subtype.

What are reified generics?

Reification & Reified Types These are called Reifiable Types, they retain their type information at runtime, because they are not subjected to type erasure. The following 2 types are NOT Reifiable Type: Exact parameterised type — List Bounded parameterised type — List

What is covariance and Contravariance in C#?

In C#, covariance and contravariance enable implicit reference conversion for array types, delegate types, and generic type arguments. Covariance preserves assignment compatibility and contravariance reverses it. string str = “test”; // An object of a more derived type is assigned to an object of a less derived type.

How do you calculate variance and covariance?

One of the applications of covariance is finding the variance of a sum of several random variables. In particular, if Z=X+Y, then Var(Z)=Cov(Z,Z)=Cov(X+Y,X+Y)=Cov(X,X)+Cov(X,Y)+Cov(Y,X)+Cov(Y,Y)=Var(X)+Var(Y)+2Cov(X,Y).