Question

Show that D defined on \(\mathrm{C}^{r}(a, b)\) by \(\mathbf{D}(f)=f^{\prime}(c)\), where \(a

Short answer

To show that the operator D defined on \(\mathrm{C}^{r}(a, b)\) by \(\mathbf{D}(f)=f^{\prime}(c)\) is a \(\phi_{c}\) -derivation, one needs to show that it is linear and satisfies the Leibniz rule with respect to \(\phi_{c}\). This can be done by making use of traditional definitions and properties of derivatives and evaluation maps.

Step-by-step solution

Verify Linearity

Firstly, to prove that D is linear, we show that for any two functions \(f, g \in \mathrm{C}^{r}(a, b)\) and any two real scalars \(\alpha\) and \(\beta\), the following holds: \(D(\alpha f + \beta g) = \alpha D(f) + \beta D(g)\). This is simply using the definitions and properties of the traditional derivative.

Prove the Leibniz Rule

Secondly, prove that the proposed form of the Leibniz rule holds for D; That is, for any two functions \(f, g \in \mathrm{C}^{r}(a, b)\), verify that \(D(fg) = D(f)\phi_{c}(g) + \phi_{c}(f)D(g)\). Here, \(\phi_{c}\) denotes the evaluation map. This again relies upon known definitions and properties of derivatives, in combination with the behavior of \(\phi_{c}\).

Conclude that D is a \(\phi_{c}\) -derivation

Since D fulfils both conditions for being a \(\phi_{c}\)-derivation, namely linearity and the specific form of the Leibniz rule, it can be concluded that D indeed is a \(\phi_{c}\) -derivation on \(\mathrm{C}^{r}(a, b)\).

Key concepts

Linearity of derivative

The concept of linearity is one of the most fundamental properties in calculus, especially when dealing with derivatives. To say that the derivative operator is linear means that for any two differentiable functions, let's consider them as function f and function g, and for any real numbers \textalpha and \textbeta, the derivative of a combination of these functions follows a specific rule. Particularly, if you have a combination such as \textalpha f + \textbeta g and you want to find the derivative, you get to distribute the derivative across the combination and multiply by the scalar values.

So in mathematical terms, this property is expressed as \(D(\alpha f + \beta g) = \alpha D(f) + \beta D(g)\). This is critical because it allows us to handle complex functions by breaking them down into simpler ones and taking derivatives piece by piece. This rule is not just a theory; you'll use this property all the time in calculus, whether you're working on homework or conducting research. It also ensures that differentiation is a scalable operation that can be applied consistently to both simple and complex functions, a feature that is essential for solving differential equations and conducting mathematical modeling.

Leibniz Rule

The Leibniz rule is a formula that describes the derivative of a product of two functions. It represents a more intricate scenario where instead of simply adding functions together, we are multiplying them. The rule is named after Gottfried Wilhelm Leibniz, a prominent mathematician who co-invented calculus.

In the context of the given \( \phi_c \) -derivation, the Leibniz rule can be tailored to the specific structure of the derivation we are looking at. Normally, the derivative of the product of two functions \( f \) and \( g \) would be \( f'g + fg' \) where \( ' \) denotes the derivative. However, in our modified case, we use the evaluation map \( \phi_c \) at a specific point c. Therefore, the product rule for our \( \phi_c \) -derivation is given by \( D(fg) = D(f)\phi_{c}(g) + \phi_{c}(f)D(g) \).

This altered rule allows you to break down the derivative of the product of two functions evaluated at a point into manageable parts, intertwining differentiation and evaluation. It's a powerful tool in calculus that extends the versatility of the derivative operator and is used, for example, when solving differential equations with initial conditions.

Evaluation map

An evaluation map is a somewhat more abstract concept compared to the more computational notions of linearity and the Leibniz rule. Essentially, the evaluation map \( \phi_c \) at a point c is a function that takes another function f and returns its value at c, so \( \phi_c(f) = f(c) \). It's as simple as plugging c into the function f and seeing what number comes out.

What's interesting about the evaluation map is that it allows us to interact with functions as if they are points. Instead of dealing with the whole function, we concentrate on one specific value that it produces. It plays a particularly critical role in functional analysis and in the context of our \( \phi_c \) -derivation, it is used to anchor the differentiation process to a particular point in the domain of the function. This gives us a localized view of differentiation, which is important when we are only interested in the behavior of our functions at specific points. The evaluation map can often simplify complex problems and is a building block for more advanced concepts in mathematics like functional calculus.