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# Star Strider

##### Last seen: Today
13,481 total contributions since 2012

Hic sunt dracones!

PROFESSIONAL: Physician (M.D.): Diplomate of the American Board of Internal Medicine; M.Sc. Biomedical Engineering: Instrumentation, Signal Processing, Control, System Identification, Parameter Estimation

NON-PROFESSIONAL: Amateur Extra Class Amateur Radio Operator; Private Pilot, Airplane Single Engine Land, Instrument Rating Airplane; Gamer

NOTE: I do not respond to emails or personal messages, unless they are about my File Exchange contributions.

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Should I use 1-D digital filtering or lowpass filter ?
Yes. Also be certain that the signals have uniform sampling intervals. If they do not, use the resample function to force them...

2 hours ago | 1

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how to solve two equations in one variable
Part of that is a differential equation. Using the Symbolic Math Toolbox to integrate it and then using matlabFunction to conve...

2 hours ago | 0

Can someone explain how this line in the code works?
The fzero call indicates that the code is to find the value of the ‘quintic’ function argument such that the function value equa...

3 hours ago | 0

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Apply a bandpass filter in freq domain
‘So I think I need to apply a bandpass filter in freq domain.’ Don’t. That is extremely difficult, since the Fourier transform...

10 hours ago | 0

Problems fitting couple differential equations to experimental data
Running your code with random data ran without error (R2020a): t = (0:20)'; f = rand(size(t)); function [x] = knfit(t,f) ...

19 hours ago | 0

How to get functions out of inputdlg
I would do something like this, using str2func and vectorize: questions = {'Enter a function of ‘x’','Enter a lower limit','En...

21 hours ago | 1

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error using ODE45 to solve a 2nd order ODE
Note that psi is the polygamma function. The code ‘overshadows’ that function with the variable name. The actual problem i...

23 hours ago | 0

1D cable model
You are calculating ‘N’ and ‘TI’. They may appear to be integers, however they are not. The solution to that is to force them ...

1 day ago | 0

Finding membrane time constant from a graph
Try adding this line to your code (after the loop): tau_Vm_num = interp1(Vm_num, time, 0.632*max(Vm_num)); so the entire code...

2 days ago | 0

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response spectrum - time domain to frequency domain
Here is some example code that you can adapt to your data: t = linspace(0, 5, 1E+4); ...

2 days ago | 0

Function handle with integrals of multiple equations?
I get different result with a strictly numeric version: V1 = 230; P1 = 2.7; T1 = 300; V2 = 30; A = -0.703029; B = 108...

2 days ago | 0

Finding the index of x values to create an equally spaced array.
Your approach appears to be correct, as far as it goes. Use the interp1 function to create your result vector: x = 0:195; y ...

2 days ago | 0

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Chebyshev type II filter
See the documentation for: cheb2ord, cheby2, zp2sos and filtfilt.

2 days ago | 0

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Suppressing only part of a function output?
To have only ‘a’ and ‘b’ returned: [a,b] = myFun(d,e) and to have only ‘c’ returned: [~,~,c] = myFun(d,e) Use variations o...

3 days ago | 0

Is there a PDF for all Matlab Functions?
There are PDF documentation for MATLAB and separately for the Toolboxes and such. For the MATLAB collection click on: PDF Docum...

3 days ago | 0

How to solve system of differential equations with time dependent parameters?
As darova suggested, integrate it numerically. For some reason, ode45 does not like the anonymous functions and throws an ’Unde...

3 days ago | 2

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Zero crossing for a curve fitting function(smoothing spline)
I don’t have the Curve Fitting Toolbox. (I only need it to reply to Answers Questions, and that’s not enough justification for ...

3 days ago | 0

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Area under FFT curve
Calculate the areas of only the ‘positive frequencies’ half of the fft output, not the entire output. If the data are all posit...

3 days ago | 0

Need to solve the roots from a large equation
Use the correct values for ‘la’ and ‘n’, then this: syms k la = 42; n = pi; Eqn = 2*k - 2*k*n + (8*k^7*n^4 - 24*k^5*n^3 + ...

4 days ago | 0

Find Middle of square wave
Use the islocalmax function (R2017b and later): This code plots green upward-pointing triangles at the centre of each pulse: ...

4 days ago | 0

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Change color of a specific line in mesh
No exact solutions without your code and data. One approach: xv = -15:0.8:15; yv = -10:0.8:10; [X,Y] = ndgrid(xv, yv); z...

4 days ago | 1

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Calculating efficiency using matlab
No loops needed: Tout = [323.2 326.0 328.8 331.6 334.3 337.1]; I = [500 550 600 650 700 750]; [Toutm,Im] = ndgrid(Tout,I...

4 days ago | 0

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Vary a parameter and plot the output
Try this: function main x0 = [500 500 500 500 5 5]; opt = optimset('Display','off'); % 'display', 'iter' I = [500 550 600 ...

5 days ago | 0

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How do I avoid using a lot of if statements in a row?
Another option is switch,case,otherwise. You will need to determine if that is an improvement over the multiple if blocks.

5 days ago | 0

Stability Analysis (Dertermining the Limit Cycle)
The phase portrait is usually plotted as the function against its derivative. Use the gradient function to calculate the deriva...

5 days ago | 0

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Peak to Peak Value of Sinusoidal Grad
Use the islocalmax function to find the maxima, islocalmin to find the minima, and go from there. (These functions were introdu...

6 days ago | 0

Solve numerically a system of first-order differential equations
Create the function symbolically: syms a b c d e f g t x(t) y(t) z(t) T Y Dx = diff(x); Dy = diff(y); Dz = diff(z); Eqn1 ...

6 days ago | 1

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Finding Angular Frequency of an Oscillation
Likely the easiest way would be to find the times of the positive peaks, then calculate from there: [pks,pktimes] = findpeaks(...

6 days ago | 1

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filter a timetable by day
I am not certain what you intend by ‘groups’. One option is to use the retime function: TTRT = retime(TT, 'daily','mean') ...

6 days ago | 0

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