Learning Integration with unit step function like u(x - a)

In summary, the conversation is discussing the integration of a function multiplied by a unit step function and the graphical representation of this concept. The conclusion is that the integral can be computed by using the antiderivative of the function without the step function and multiplying it by the unit step function and the difference between the upper and lower limits. The conversation also touches on the importance of including the unit step function in the integral to accurately represent the function's behavior.
  • #1
hanhao
20
0
hello maths experts
is the following true?
http://img9.imageshack.us/img9/4596/int15oe.jpg

graphically, this is how i view it
http://img9.imageshack.us/img9/179/int28ut.jpg
 
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  • #2
Yes, that's pretty much correct, but the right hand side is missing a "+C" because it is an indefinite integral.
 
  • #3
how about this?

http://img108.imageshack.us/img108/1626/38jk1.jpg
is u(x-a) redundant? can i remove it like this?
 
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  • #4
hanhao said:
how about this?

http://img108.imageshack.us/img108/1626/38jk1.jpg
is u(x-a) redundant? can i remove it like this?
No, the integral is constant for x<a. The u(x-a) keeps the part of the integral that is dependant on x zero for x<a, so it is just the constant of integration before that. The integral should be u(x-a)[F(x)-F(a)]+C.
 
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  • #5
i want to understand this graphically
how would the graph of u(x-a)[F(x)-F(a)] look like compared to [F(x)-F(a)] ??
am i correct to say that my bottom graph is [F(x)-F(a)] ??
 
  • #6
I am assuming you mean the bottom graph in this image, so tell me if I am wrong:
http://img9.imageshack.us/img9/179/int28ut.jpg
This is not the graph of [F(x)-F(a)]. The function itself is f(x)u(x-a). The area represents the integral of this, which is u(x)[F(b)-F(a)], where b is the upper limit.

[F(x)-F(a)] represents an antiderivative of f(x) without the step function. Suppose b and c are both less than a. Obviously the integral,I, of f(x)u(x-a) from b to c is zero, but look what happens when you plug this into the function you proposed:
I=[F(c)-F(a)]-[F(b)-F(a)]=F(c)-F(b)
which is not necessarily zero.
 
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  • #7
We have limits between infinite to minus infinite how can i compute when i multiply a function with an unit step function. i mean i have an integral the limits of that integral is infinite to minus infinite and inside the integral i have f(t).u(t-a) this. So how can i compute this integral ?
 

1. What is a unit step function?

A unit step function, denoted as u(x-a), is a piecewise function that equals 0 for all x < a and 1 for all x > a. It represents the sudden change in value at a specific point a.

2. How is a unit step function used in learning integration?

Unit step functions are used in learning integration as a way to break down complex functions into simpler pieces. By using the unit step function, we can split a function into two parts and integrate each part separately.

3. What is the significance of the point a in the unit step function?

The point a in the unit step function represents the point at which the function changes from 0 to 1. This point is also known as the step or jump point and is used to divide the function into two separate parts for integration.

4. Can a unit step function be used in integration for functions with multiple variables?

Yes, a unit step function can be used in integration for functions with multiple variables. In this case, the step function would depend on the specific variable being integrated and would have different values for different variables.

5. How can I practice and improve my skills in learning integration with unit step functions?

There are several ways to practice and improve your skills in learning integration with unit step functions. You can solve practice problems, work through examples, and seek help from a teacher or tutor if needed. Additionally, using online resources and interactive tools can also be helpful in understanding and mastering this concept.

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