# Tag Info

### Alias frequency Formula

One easy formula: $$f_{a} = \text{sign}(f) \; \cdot \; \left( |f| - \Big \lfloor \frac{|f|}{f_{\text{nyq}}} \Big\rfloor \; \cdot \; f_{\text{nyq}} \right)$$ where $f_{a}$ is the aliased frequency, ...
• 600

### How do you find the null to null bandwidth for the signal below?

The $\text{sinc}$ function is the Fourier Transform of a Rectangular pulse. Its zeros are located at non-zero integers of $x$. Therefore, if your spectrum can be expressed as $\text{sinc}(Bx)$, the ...
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### How do you find the null to null bandwidth for the signal below?

The key observation is that $\text{sinc}(x)$ is zero for all arguments $x$ that are nonzero integers, so the problem reduces to "what values of $f$ yield the nonzero integers closest to zero, ...
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### How do you find the null to null bandwidth for the signal below?

The following MATLAB script is a solution to your question clear all;close all;clc 1. fzero only returns 1 zero ...
1 vote

### What are some approaches / algorithms for reducing size of numerical data of large size with redundancies?

You have two issues here: Number 1: your format is very inefficient. If you convert this from Ascii to a suitable binary format, you can probably reduce the size by a factor of 4 or so. Number 2: your ...
• 34k
1 vote

### What are some approaches / algorithms for reducing size of numerical data of large size with redundancies?

What makes this dataset so big is not per se the number of samples. In your case, it's the ASCII format*. You should just convert the data to 32bit (or even just 16bit or lower, depends on the ...
• 1,922
1 vote

### Algorithm to detect down-up-down pattern in time series

Step 1: Low Pass Filter Step 2: 2nd derivative. The 2nd derivative gives you the curvature. Step 3: If it switches sign three times, check the values at those points to confirm they're actual peaks. ...
• 123
1 vote

### Algorithm to detect down-up-down pattern in time series

Can you narrow down how the plot should generalize? Ie how much variation do you expect for the time between edges and absolute step height? What might noise (variable stuff that should lead to no ...
• 2,412

### Algorithm to detect down-up-down pattern in time series

Very first thought here: Aggressive Low Pass (to get the trend, would be a pretty low cut-off you can experiment with). Local maxima and minima detection (you can use the 1st derivative's 0-crossings ...
• 1,033
Accepted

• 34k
1 vote

### How do I determine if the fundamental period $T_{x}$ exists and if so what it is?

All (finite-energy) periodic signals can be represented by Fourier series which consist of a sum of harmonics of a fundamental frequency $\omega_0$. Some of the various harmonics as well as the ...
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