# 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) ...

ongeveer 2 jaar 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 ...

ongeveer 2 jaar ago | 0

| accepted

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.

ongeveer 2 jaar 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...

ongeveer 2 jaar 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...

ongeveer 2 jaar ago | 0

| accepted

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...

ongeveer 2 jaar ago | 2

| accepted

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...

ongeveer 2 jaar 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 ...

ongeveer 2 jaar 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 ...

ongeveer 2 jaar 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(...

ongeveer 2 jaar ago | 0

| accepted

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 -...

ongeveer 2 jaar ago | 1

Submitted

fitellipse.m

Fit ellipses to 2D points using linear or nonlinear least squares

bijna 6 jaar ago | 36 downloads |

Submitted

nearestneighbour.m

Computes nearest neighbour(s) by Euclidean distance

bijna 6 jaar ago | 12 downloads |

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...

meer dan 8 jaar 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); ...

meer dan 8 jaar 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...

meer dan 8 jaar 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...

meer dan 8 jaar 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...

meer dan 8 jaar ago | 0

| accepted

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...

meer dan 8 jaar ago | 0

| accepted

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...

meer dan 8 jaar ago | 0

| accepted

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...

meer dan 8 jaar ago | 5

| accepted

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...

meer dan 8 jaar 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 ...

meer dan 8 jaar ago | 2

| accepted

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...

meer dan 8 jaar 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...

meer dan 8 jaar 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)|...

meer dan 8 jaar 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...

meer dan 8 jaar 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...

meer dan 8 jaar 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;...

meer dan 8 jaar ago | 2

please help with logical operators

replace all instances of |lenght| with |length|

meer dan 8 jaar ago | 0