# Richard Brown

### Massey University

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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**Content Feed**

Alternatives to Delaunay triangulation

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

2 years ago | 1

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 ...

2 years ago | 0

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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.

2 years ago | 1

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...

2 years ago | 0

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...

2 years ago | 0

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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...

2 years ago | 2

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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...

2 years ago | 0

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 ...

2 years ago | 1

| accepted

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 ...

2 years ago | 1

| accepted

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(...

2 years ago | 0

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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 -...

2 years ago | 1

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...

8 years ago | 0

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); ...

8 years ago | 2

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...

8 years ago | 1

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...

8 years ago | 0

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...

8 years ago | 0

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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...

8 years ago | 0

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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...

8 years ago | 0

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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...

8 years ago | 5

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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...

8 years ago | 1

| accepted

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 ...

8 years ago | 2

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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...

8 years ago | 0

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...

8 years ago | 0

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)|...

8 years ago | 1

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...

8 years ago | 0

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...

8 years ago | 2

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;...

8 years ago | 2

please help with logical operators

replace all instances of |lenght| with |length|

8 years ago | 0

End of function slow - Matlab Profiler

Pretty sure you'll find it's the overhead for the function call

8 years ago | 0

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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...

8 years ago | 0