# Why am I here?

If you were sent here, somebody thought that you posted your question too early, that is you don't know facts and/or techniques one would learn in undergraduate courses. This is not your fault, but for us who write answers it has become a chore to explain the same things over and over again (many such questions arise from homework, and homework problems do not differ a lot).

Therefore, we would like you to go over your course material again (if you are a student) or peruse material readily available in libraries or the web. Chances are you will be able to answer or at least improve your question with your new knowledge!

In order to help you with that, we have compiled a list of questions that are of general nature and have answers that should apply in a variety of situations. Please take the time to browse through those relevant to your question; chances are that we already have you covered. If not, it is likely that one of two things has happened:

1. You don't understand the reference material.
In this case, the best response is to do further research. That includes picking up textbooks (the reference answers may list some) and asking focused questions on the main site.

2. You understand the material, but you can not apply it to your situation.
In this case, edit your old question to include your attempts at solving the problem and why they failed. Then flag it for reopening; with this new information, we can help you identify your specific problem and move forward.

Remember: "I don't understand any of this, please explain in plain English!" is a bad inquiry. Nobody can know what your problem really is, which factoid would help you understand, and what the required scope for a good answer is. Try instead to phrase questions like "In above solution, why does B follow from A?" or "I have an algorithm but it seems to be wrong for corner case X, how can I fix it?"

That said, you find links to the reference posts grouped by topic below:

$${\tiny\mbox{ This text stolen from CS.SE.}}$$

# Impulse Response

The impulse response, $$h(t)$$, of a linear, time-invariant (LTI) system describes the relationship between input and output via convolution: $$y(t) = h(t) \star x(t)$$

# Image Processing

Image processing is the area of signal processing dealing with two-dimensional signals that represent color or grayscale images.

# Change Detection

Change detection is when a signal is being observed and the time of a particular change in the signal is needed to be known / detected.

# Frequency Spectrum

The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain.

# Filtering

Filtering is a way to process an input signal so that the output signal has interesting features enhanced or unwanted features reduced.

# Fourier Transform

The continuous-time Fourier transform of a time-domain signal $$x(t)$$ is

$$X(\omega) = \int_{-\infty}^{+\infty} x(t) e^{-\jmath \omega t} dt$$

# Homework Questions

Some questions are closed with the reason:

This question appears to be homework. Complete answers to homework are off-topic, but specific questions about homework are acceptable if they include enough detail. Please edit the question to include more background about what you don't understand.

That doesn't mean we won't answer homework questions, but that you should put as much detail as you can with your current answer to show the reader where your understanding breaks down.

## What to do if your question is closed

Whatever you do, please engage with the feedback! Please edit your question and try to add your attempt to solve the problem. If you can, please express what you don't understand or what you think you're missing.

That way, we can help, but not spoon feed you the answer.

# My Questions Keep Getting Closed

The StackExchange series of websites is a Question & Answer site. Some questions do not have definitive answers or require an opinionated answer. That sort of question, which requires much discussion, does now lend itself to this site.

Other places you might be able to get a discussion are: