# Christoph F.

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**Content Feed**

sos2tf: different result in filtfilt by using SOS vs tf

> IIR Butterworth bandpass of order 40 IIR filters with orders this high are fairly susceptible to numerical effects like coe...

5 years ago | 1

| accepted

Applied Fft to my temperature sensor readings and don't understand the result

> Is there an explanation for this result, or is it wrong. The result looks correct. The Fourier transform shows a large DC c...

6 years ago | 0

| accepted

Why do I get different frequency response using state-space representation and transfer function

124th order recursive filters are iffy, numerically. At this point, the limited precision of even the double datatype can lead t...

6 years ago | 1

I am getting error Undefined function or variable, How to solve this error??

The error means MatLAB cannot find the function write_grid_images(). Is it defined in a separate file or in the same file as ...

6 years ago | 0

what is wrong in my code trapezoidal rule

Curly brackets {} have a special meaning in MatLAB syntax (usually when you want to work with the cell datatype). If you did ...

6 years ago | 0

| accepted

Writing large ammount of data over serial is very slow

A baud rate of 250000/s means a transfer rate of roughly 21000 bytes/s. This means sending 960000 bytes will take about 46 secon...

6 years ago | 0

why are the peaks of FFT of generated signal slighty off?

Multiplying a function with another function can change the frequency content, as this corresponds to convolving the two image f...

6 years ago | 0

XCORR of two harmonic signals has a triangular shape. Why?

> What can be the reason of such triangular shape? The reason is that both signals have a significant DC component/offset. Tr...

6 years ago | 1

How can i use Moving Average Filter to change the sampling rate of a signal!?

You filter the signal and then you reduce the sampling rate. In the most simple case: X=filter([0.5 0.5], 1, X); % Two-e...

6 years ago | 0

| accepted

Why does the code output something that's clearly false?

> Why is this happening? Look at the value of Ai-AT MatLAB uses numeric methods to invert matrices with inv(), and nu...

6 years ago | 0

| accepted

Designing a Chebyshev type 2 filter directly in the discrete-time domain?

Answering my own question: The missing criterion is indeed related to the maximum flatness - the second derivative of the sq...

6 years ago | 0

| accepted

Question

Designing a Chebyshev type 2 filter directly in the discrete-time domain?

I am trying to design a Chebyshev type 2 filter in the discrete-time domain in order to have control over the placement of the f...

6 years ago | 1 answer | 0

### 1

answerPlot ECG based on heart rate

> I'm having problems getting the plot to display in seconds rather than samples. It looks like your t vector is in samples ...

6 years ago | 0

Checking for divisibility?

> Is this a result of rounding error? No, it is the result of a bug. In your while loop, the code inputs a new value for cash...

6 years ago | 0

What does the error Attempted to access k(3e-10); index must be a positive integer or logical. mean?

k(a+b) means to MatLab "the (a+b)th element of vector k". However, a+b isn't integer. Maybe the expression cos(k(a+...

6 years ago | 0

Speed up FIR filter

As an answer: Using filter() instead of filtfilt() to apply the filter will speed up the calculation by an order of magnitude...

6 years ago | 1

how to smooth Fourier Spectrum of an acceleration-time history

To make the spectrum appear smoother, you can either apply a window function to the signal in the time domain by element-wise mu...

6 years ago | 0

How can I do a backward only bandpass filter

Reverse the signal vector, apply bandpass filter with the filter() command, reverse the result?

6 years ago | 0

I have question of FFT(fast fourier transform)

A Fourier transform decomposes a time-domain signal into sinusoidal components. The frequencies of the sinusoidal components are...

6 years ago | 1

How to count if loops

count=0 loopStart=1 loopEnd=6 while loopStart < loopEnd count = ...

6 years ago | 0

| accepted

Finding the exponential of a very small number

> This is not right. Is is as close to the correct answer as can be represented with the 64-bit floating point format that Ma...

6 years ago | 2

Code Optimization, for loop

Two suggestions: The inner loop only loops from Tmin to (m-1). The extra comparison of m and i inside the loop could be remov...

6 years ago | 0

| accepted

Get time signal back after NFFT

The time vector as as many elements as X, and they are spaced 1/(f(2)-f(1)) apart. And you will probably need to reverse the ...

6 years ago | 0

detect QRS signal from ekg shield

If the ECG is noisy, the first place to look for issues would be the circuitry and the connection to the patient. Electrode cont...

6 years ago | 1

The output of my PID controller is coming very high...

Without more information, perhaps the simulink diagram, the question will be difficult to answer. In general, PID controllers...

6 years ago | 0

How can I remove noise from my graph?

The most straightforward option is using a filter to remove the noise. This works if the noise has a different spectral content ...

6 years ago | 0

Want to use Matlab similar to Solver in Excel

I think you're looking for the fminsearch() function. Or alternatively something from the curve fitting toolbox.

6 years ago | 0

get inverse fourier Optimization, how can i do?

The "clean" solution would be to use MATLABs fft()/ifft() functions. They are optimized and also work for vector sizes that are ...

6 years ago | 0

How concatenate several signals

> If I do x = [x ; x ], x is a row vector. To concatenate row vectors, use x=[x x] [x; x] creates a 2-by-lenght(x) m...

6 years ago | 0

Why is MATLAB officially written with capitalized letters?

Because it's a trademark (and hence should be recognizable)?

6 years ago | 1