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David Wilson


Auckland University of Technology

93 total contributions since 2011

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Answered
fitting scatter data into multiple cosine functions
Yes, but it is always tricky to fit such sinusoids without good starting estimates. I'm going to use lsqcurvefit from the optimi...

3 days ago | 0

Question


Is the Moving Variance block in Simulink vectorised?
I'm using the Moving Variance block in Simulink and it seems to be giving unexplained results for vectorised (muxed) inputs. My ...

10 days ago | 0 answers | 0

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answers

Answered
2D Convolution - Sobel Filter. What is wrong?
Here's my (old) code for a sobel filter: img = imread('Davis_Hall.jpg'); % 'Davis_Hall.jpg':color image X =double(rgb2gray(i...

1 month ago | 0

Answered
Related to Matlab Step Comment
You are possibly confusing the closed loop response with the open loop. The closed loop gain is 1/4, so the error is 1-1/4 = 3/4...

2 months ago | 1

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Answered
how to solve matrix differential equation
Here's my attempt: M = [ 97227/21875, 0, 82269/109375, 0, 67311/43750, 0, -97227/218750, 0; ... 0, 97227/21875, 0, 822...

2 months ago | 1

Answered
From Fir2 output to transfer function
tr_fun should be a discrete transfer function, (not continuous) say tr_fun=tf(BF,1,1); % Generate a DISCRETE Transfer Function...

2 months ago | 0

Answered
How to identify corners of data plotted to estimate data between corners
How about using interp1 with the 'pchip' option? You did speculate the interpolation is overly complex, but then again it is onl...

3 months ago | 1

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Answered
How I can find co ordinates of intersection of two curves ?
Oh, looks like this is a common question: See (from 2016)https://au.mathworks.com/matlabcentral/answers/318475-how-to-find-the-i...

3 months ago | 1

Answered
Iterative Method of solving multiple variables without using the curvefit tool
Here's my attempt at fitting uusing lsqcurvefit from the optimisation toolbox. First I generate some synthetic data to subsequ...

3 months ago | 0

Answered
how can i calculate the angle of each gradient and x axis?
You could always differentiate to get the slope and then take the arc-tan. syms x real s = 1/(1 + exp(-2*(x-4))) dsdx = dif...

3 months ago | 0

Answered
Extracting the daily time series from a text file to a single column
A quick hack is: fname = 'D59.txt' Flow = []; fid=fopen(fname); Yr = 2012; R = []; while 1 tline = fgetl(fi...

3 months ago | 0

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Answered
How to Rearrange data?
Try something like the following: First read in the data file (which I've called numData.txt). I've used your test data above. ...

4 months ago | 0

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Answered
(Food for Thought) Peak Detection on ECG signal
OK, here's my (ugly) solution (withou using findpeaks). I've re-named your data set, and did some pre-processig. load ecg y =...

4 months ago | 0

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Answered
Simulating a FIR filter
Use the filter command. In this case your denominator, (A), coefficients are just 1. x = [ 0 0 0 1 1 1 1 1 ]' % input b = [...

4 months ago | 1

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Answered
Obtain input knowing output and transfer function
Since you have a simple transfer function, here's what I would do. (1) First generate some data that we will subsequently try ...

4 months ago | 0

Answered
curve fitting of non linear data for strain-time of creep experiment
Here's my attempt: load data1 t = time; e = strain; plot(t,e) %% Now try curve fit creep = @(p, t) p(1)*(1-exp(-p...

5 months ago | 0

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Answered
Trouble with time delay differential equation
I've only made one small change to your function. You have tried to index a non-integer number back, but the "Z" variable holds ...

5 months ago | 0

Answered
How can I simultaneously solve for these equations?
If you have the symbolic toolbox, a straight forward approach works, although it takes some time ... % ODE propblem syms B...

5 months ago | 0

Answered
Error when using ode15
It is good practice to try and avoid globals, but rather pass them as auxilary variables into the function. Fao = 1487.351; % ...

5 months ago | 0

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Answered
Plotting Step Response of a Differential Equation
You are close to a viable solution. Solve for an analytical solution, then make it a Matlab (anonymous) function with matlabFunc...

5 months ago | 0

Answered
Runge-Kutta 4th order method
First up, you will need a much smaller step size to get an accurate solution using this explicit RK4 (with no error control). I ...

6 months ago | 0

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Answered
How to draw Fig. 1 from the attached pdf with this code
I didn't bother draw the other 3 lines, but you just ned to make the necessary changes to gamma for that. If you run somethi...

6 months ago | 0

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Answered
fsurf not drawing cant explain
Do you really need to use the symbolic toolbox? Why not just plot a numerical surface? But you are right, your numbers are widel...

6 months ago | 0

Answered
Fitting Monod Equation with ODE45 to data using lsqcurvefit function
Here's my solution. First set up the measured data, plot it, and look to see that it is all OK. t = [0 3 5 8 9.5 11.5 14 16 ...

6 months ago | 0

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Answered
Solve integrals with Matlab
Do you have the symbolic toolbox? If so, start with the int command. You can do both indefinite and definite integration. sy...

6 months ago | 1

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Answered
MATLAB Help - Rolling Dice Simulation / Central Limit Theorem
A quick hack using randi and cumsum is N = 100 x = randi(6,N,6); cs = cumsum(x')'; for i=1:6 subplot(3,2,i) histogram...

6 months ago | 0

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Answered
How to calculate the accumulated rainfall value of 1, 2, 3, 4, 5, 6 and 7 days.
Here is my solution: I notice that you've got few NaNs for about a year and a half. Your last year is also incomplete. I is...

6 months ago | 0

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Answered
plot x axis as persentage
Below, I've plotted an arbitrary function between arbitrary limits, -5 and +37. %% x = linspace(-5,37)'; y = erf(x/20); ...

6 months ago | 0

Answered
inline function error help(tanh)
I can, but perhaps you should use anonymous functions. The inline approach is now discouraged. Instead of what you wrote above...

6 months ago | 0

Answered
how to plot multiple waves on one surface
Here is a mock up solution. Code is: below. I've used part of your data, but I've made up some similar data (using a sinc fun...

6 months ago | 0

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