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Richard Brown


Massey University

Last seen: oltre un anno fa |  Attivo dal 2008

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Maths Lecturer at Massey University. Working on high performance computing and modelling. Professional Interests: numerical analysis, modelling, computer vision, mathematical biology

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Risposto
Alternatives to Delaunay triangulation
As David Wilson suggested, use alphashape: U = csvread('Coords.txt'); shp = alphashape(U(:, 1), U(:, 2), U(:, 3)); plot(shp) ...

circa 5 anni fa | 1

Risposto
How to pass a method as a function handle
I think the issue is that to use the @ construction, the thing you're applying it to needs to be named function in scope. There ...

circa 5 anni fa | 0

| accettato

Risposto
Singular Matrices: Is the Matlab algorithm for CONDITON NUMBER always stable ?
The algorithm for condition number uses the SVD, not LU factorisation and is perfectly stable.

circa 5 anni fa | 1

Risposto
3D Measurementm using matlab
You could try the computer vision toolbox, which has an interface to OpenCV I believe. Writing the whole thing from scratch is...

circa 5 anni fa | 0

Risposto
Taking Mean Of Specific Rows and Columns Within A Loop
You don't need a loop. Basic idea: extract column 2. Reshape it into a matrix with columns 1200 tall take the mean of each co...

circa 5 anni fa | 1

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Risposto
Need to solve the differential equation for beam deflection and get the following plot
I think the problem you're having is not fully figuring out your solution before diving in and coding it. You have a differentia...

circa 5 anni fa | 2

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Risposto
How to go around infinite recursions
I'm not sure the code you've written describes what you intend. It's going to create an unterminated recursion that will cause a...

circa 5 anni fa | 0

Risposto
need help with basic speed time graph plot
Your function needs to have elementwise powers, i.e. use .^ instead of ^ It's trying to do matrix powers of the vector of time ...

circa 5 anni fa | 1

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Risposto
Random sampling of elements from an array based on a target condition in MATLAB
If your process is just to sample until you are within a tolerance of V_1 and you want things to be truly random, how about the ...

circa 5 anni fa | 1

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Risposto
For a class object with a property that is an array of class objects, how to find the element in that array with highest property value
Your obj.population.fitness line returns comma separated values, not an array. So just enclose it in brackets: [M, I] = max(...

circa 5 anni fa | 1

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Risposto
Non Zero element appear first with keeping the same size of the matrix?
here's a really naive way to do it: [m, n] = size(A); for i = 1:m k = find(A(i, :)) A(i, :) = [A(i, k), zeros(1, n -...

circa 5 anni fa | 1

Risposto
How to create a sparse matrix with such specifications?
*edit* This version is wrong, but leaving so comment below makes sense density = 0.01; % For example m = 10000; n = 1000...

oltre 11 anni fa | 0

Risposto
count groups of elements and distances between them
A = [6 6 6 4 4 4 4 4 6 5 5 7 7 7 8 9 8 7 0 0 0 0]; x = diff([find(diff([0 ismember(A, [0 6]) 0]))]); L = x(1:2:end); ...

oltre 11 anni fa | 2

Risposto
Positive Semi-definite Matrix Problem
You're just going to have to live with it. Your matrix is PSD to double precision. If you look at the magnitude of the "zero" ei...

oltre 11 anni fa | 1

Risposto
vectorizing calculation of eigen values of a large multi-dimensional array
You'll get a bit of a performance boost simply by looping over linear indices rather than nesting (this is more than twice as fa...

oltre 11 anni fa | 0

Risposto
Reduced row echelon form technique
It'll be a difference between yours and MATLAB's choice of tolerance. Your matrix should be rank 2, however I notice that MATLAB...

oltre 11 anni fa | 0

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Risposto
Evaluation of matrix element of a linear differential matrix equation by constrained least square fitting
Assuming you have multiple |X| and |X'| vectors that you're trying to fit your matrix to, your problem can be posed as a constra...

oltre 11 anni fa | 0

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Risposto
displaying indexed values correctly
Similar to what you asked before, I think what you want is to find the |Vb| element that is closest to half of |Vb_ev|, and then...

oltre 11 anni fa | 0

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Risposto
finding closest values in array
If I understand correctly, you want to find the |pH| value in your array closest to 4.756, and pull this value out, together wit...

oltre 11 anni fa | 5

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Risposto
How can I create sparse symmetric positive definite linear system?
|sprandsym| is what you want. m = 50; density = 2/m; % for example rc = 0.1; % Reciprocal condition number A = spr...

oltre 11 anni fa | 1

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Risposto
Sign differences in QR decomposition
It's only unique up to the signs of the rows of |R|. If you want to enforce positive diagonals of |R|, and thereby get a unique ...

oltre 11 anni fa | 3

| accettato

Risposto
Output argument "Clus_Area" (and maybe others) not assigned during call to
Check that the line if AR > 0 is doing what you intend. This will only evaluate if all entries of |AR| are positive. T...

oltre 11 anni fa | 0

Risposto
How to use variable value as an input to the function?
You can very probably get away with just passing |template1| and |template2| themselves (not trying to create references to them...

oltre 11 anni fa | 0

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Why I'm keep getting these errors? Please help!
The error message says it all. You're only computing one derivative in |my_function|. You need to define |ys(1)| and |ys(2)|...

oltre 11 anni fa | 1

Risposto
How do I efficiently calculate a scalar distance with 3d geometry?
You should use |hypot|. It also has better numerical stability. *edit* sorry, you're in 3D. That obviously won't work. You c...

oltre 11 anni fa | 0

Risposto
Generating a particular sequnce of numbers
Also comparable, but not (quite) faster n = 1:(d*(d+1)/2); a = ceil(0.5*(-1 + sqrt(1 + 8*n))); out = a.*(a + 1)/2 - n...

oltre 11 anni fa | 2

Risposto
Generating a particular sequnce of numbers
Even faster: k = 1; n = d*(d+1)/2; out = zeros(n, 1); for i = 1:d for j = i:-1:1 out(k) = j;...

oltre 11 anni fa | 2

Risposto
please help with logical operators
replace all instances of |lenght| with |length|

oltre 11 anni fa | 0

Risposto
End of function slow - Matlab Profiler
Pretty sure you'll find it's the overhead for the function call

oltre 11 anni fa | 0

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Risposto
Fit and Plot Gaussian Function
Sure, rather than trying to fit a distribution (which is not what you want), just fit the Gaussian itself. Generate some nois...

oltre 11 anni fa | 0

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