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Matt J


Last seen: Today
6 905 total contributions since 2009

Professional Interests: medical image processing, optimization algorithms

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Answered
Vectorization or for loop (speedup)
Your vectorized code doesn't resemble at all what your for-looped code is computing. The vectorized implementation of your for-l...

37 minutes ago | 0

Answered
In nested for-loops, how and where should I set the counting index (indices?) correctly, for doing numerical root-finding using fsolve?
Well, first of all, you would not use fsolve when doing a gridded root search. In general, the search could be done like this: ...

environ 5 heures ago | 1

| accepted

Answered
Caclulate Horizonzal Area Between Two Curves And Minimize This Area (Optimization Problem)
The analytical solution to the problem is to take the shift x which maximizes the correlation of C and D https://en.wikipedia.o...

environ 5 heures ago | 0

Answered
how to find the right distance evaluation function of an ellipse
See this related thread, https://www.mathworks.com/matlabcentral/answers/555925-does-anyone-know-how-to-use-the-matlab-to-calcu...

environ 5 heures ago | 0

Answered
Plot a 2D image in projected coordinate systems.
I do not understand how a 3*10095 matrix is being interpreted as an image. You don't to have any pixel values, as far as I can s...

environ 7 heures ago | 0

Answered
Configure Matlab to use Python without pyenv
Mario's solution worked!

environ 21 heures ago | 0

| accepted

Answered
How to perform logical AND on intervals of contiguous locations
Using group1s from https://www.mathworks.com/matlabcentral/fileexchange/78008-group1s >> xg=group1s(x)+1; >> yg=splitapply(@a...

1 jour ago | 0

Answered
How do you create a matrix of matrices?
Put your 10x10x10 arrays in cells https://www.mathworks.com/help/matlab/cell-arrays.html Example: >> A{3,3}=rand(10,10,10) ...

1 jour ago | 0

| accepted

Question


Configure Matlab to use Python without pyenv
I am trying to call Python from Matlab R2019a on a Windows 10 PC. I have Python 3.7 installed under Spyder 3, but Matlab cannot ...

1 jour ago | 1 answer | 1

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answer

Answered
Sub-matrix Access in a Square Pattern
Using mat2tiles from https://www.mathworks.com/matlabcentral/fileexchange/35085-mat2tiles-divide-array-into-equal-sized-sub-arr...

3 jours ago | 0

Answered
Add for each element of a matrix the column vector in another dimension
Hi!i have a matrix 136*136. Call this A. This value is the index of a column of another matrix(24*391) Call this B. Then, re...

3 jours ago | 1

| accepted

Answered
a 6x6 matrix with unkown x
See eig().

3 jours ago | 0

Answered
local optimisation deterministic optimisation
fvalue = 50 is clearly a better (i.e. lower) objective value than 212.5, so there is every reason to believe that x1=42.5 x2=5...

3 jours ago | 0

Answered
Failure in initial objective function evaluation. FMINUNC cannot continue. Need some help
You have set SpecifyObjectiveGradient=true, but your objective function code does not provide a second output for your gradient ...

4 jours ago | 2

Answered
Does Matlab have an off-the-shelf function to generate a 2D circular convolution matrix?
You can use func2mat from https://www.mathworks.com/matlabcentral/fileexchange/44669-func2mat-convert-linear-function-to-matrix...

4 jours ago | 0

Answered
Do numerical solutions depend on lower and upper bounds even when those bounds are not binded?
Changing the bounds affects where the algorithm can search, which can change the sequence of iterations, which can change which ...

4 jours ago | 1

| accepted

Answered
What is considered good practice for coding up a function's derivatives, e.g. its Jacobian and Hessian matrices?
However, I imagine it's not best practice to continue doing this, especially when I start considering many more variables, and t...

4 jours ago | 1

| accepted

Answered
How to compute cost function for fmincon?
r=[0.22 9.94 0.08; 0.16 0.95 0.08; 0.07 0.87 0.08]; R = [0.49; 0.42; 0.19]; omega=0.1; gamma=150; fun=@(x) norm( ...

4 jours ago | 1

| accepted

Answered
Dividing 3D image to 3D patches
Using mat2tiles, https://www.mathworks.com/matlabcentral/fileexchange/35085-mat2tiles-divide-array-into-equal-sized-sub-arrays ...

5 jours ago | 0

| accepted

Answered
How to apply Loop Function to this example
x=x0; for i=1:10 x=M*x; end

6 jours ago | 0

| accepted

Answered
Question on GPU Computing
Make sure you have updated drivers and make sure you restart your computer after their installation. Then use gpuDevice() to sel...

6 jours ago | 0

Answered
How to find the length of a curve from a list of points using different length scales?
curveLength = sum(vecnorm( diff( [x(:),y(:)] ) ,2,2))

6 jours ago | 0

Answered
Creating matrix with other matrix
[a(:,2:3),b(:),c]

6 jours ago | 0

| accepted

Answered
abcd is efghijk?
function C= circulant(x) n=length(x); C=zeros(n,n); C(1,:)=x; for i=2:n C(i, :)=[C(i-1, n) C(i-1,...

7 jours ago | 1

Answered
parfor problem (broadcast variable)
There's never any gaurantee parfor will be faster, but I would modify the code as follows, B_Data=A_Data(:,2:5)/(0.6*2); B_ref...

7 jours ago | 0

Answered
Use inpolygon command for multiple polygon areas
Use discretize(), https://www.mathworks.com/help/matlab/ref/double.discretize.html Apply it separately to all of your xv's and...

8 jours ago | 0

Answered
For loop and array type
Best guess - your loop has reached a z for which allcsvfiles{z,1}(:,4) contains text. Use dbstop() to check.

8 jours ago | 0

Answered
Array of Structures (not structure array)
I don't know if this is something you explored in (2), but if so, I don't see why it wouldn't cover what you are trying to do. ...

8 jours ago | 0

Answered
Memory cost of multiplying sparse matrices
Here's another customized multiplication routine for tall A. I do not know how it compares to Bruno's in terms of speed, but it ...

10 jours ago | 0

Answered
Memory cost of multiplying sparse matrices
I believe it is simply because Matlab sparse matrix routines don't handle very tall & thin matrix dimensions very well. It beco...

11 jours ago | 0

| accepted

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