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Richard Brown


Massey University

202 total contributions since 2008

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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Submitted


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

etwa 3 Jahre ago | 49 downloads |

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Submitted


nearestneighbour.m
Computes nearest neighbour(s) by Euclidean distance

etwa 3 Jahre ago | 56 downloads |

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Answered
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...

mehr als 5 Jahre ago | 0

Answered
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); ...

mehr als 5 Jahre ago | 2

Answered
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...

mehr als 5 Jahre ago | 1

Answered
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...

mehr als 5 Jahre ago | 0

Answered
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...

mehr als 5 Jahre ago | 0

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Answered
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...

mehr als 5 Jahre ago | 0

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Answered
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...

mehr als 5 Jahre ago | 0

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Answered
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...

mehr als 5 Jahre ago | 5

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Answered
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...

mehr als 5 Jahre ago | 1

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Answered
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 ...

mehr als 5 Jahre ago | 1

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Answered
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...

mehr als 5 Jahre ago | 0

Answered
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...

mehr als 5 Jahre ago | 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)|...

mehr als 5 Jahre ago | 1

Answered
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...

mehr als 5 Jahre ago | 0

Answered
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...

mehr als 5 Jahre ago | 2

Answered
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;...

mehr als 5 Jahre ago | 2

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

mehr als 5 Jahre ago | 0

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

mehr als 5 Jahre ago | 0

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Answered
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...

mehr als 5 Jahre ago | 0

Answered
Surface area from a z-matrix
OK, well how about splitting each quadrilateral into two triangles, and just summing up the areas? I'm sorry there's no way I ca...

fast 6 Jahre ago | 0

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Answered
Argmin with several minimums
It doesn't feel very satisfactory, but this will do the trick I = find(A == min(A))

fast 6 Jahre ago | 0

Answered
Projecting Points to a new Basis
I'm not sure what your question is asking because you're missing a symbol off your question. But I think you mean if n is not eq...

fast 6 Jahre ago | 0

Answered
How can I use "symbfact" to speed up several consecutive Cholesky factorizations?
You can't (unless something has changed recently). When I had to do this, I ended up working with the C code in CSparse directly...

fast 6 Jahre ago | 0

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Answered
Simple solution to a simple problem
Try 1./(1 + 9*x.^2) i.e. a '.' before the division

fast 6 Jahre ago | 0

Answered
Piecewise Cubic Hermite Interpolating Polynomial (PCHIP)
It works perfectly x = [5.8808 6.5137 7.1828 7.8953]; y = [31.2472 33.9977 36.7661 39.3567]; pp = pchip(x...

fast 6 Jahre ago | 0

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Answered
Sparse and nonspare QR
Sorry to take a while, busy week. Neither are wrong. You'll notice that the only difference in the outputs is that the sparse ve...

fast 6 Jahre ago | 0

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Answered
Sparse and nonspare QR
On my system they match (up to the signs of the rows, as you'd expect). m = 20; n = 10; X = sprand(m,n,0.3); Rs...

fast 6 Jahre ago | 0

Answered
How to calculate expm of a badly scaled matrix?
You might this Cleve's corner instructive <http://blogs.mathworks.com/cleve/2012/07/23/a-balancing-act-for-the-matrix-exponenti...

fast 6 Jahre ago | 0

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