Matt J

Last seen: 1 day ago

7,896 total contributions since 2009

Professional Interests: medical image processing, optimization algorithms

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Answered
How can I find exactly the coordinates of the center of the yellow circle?
regionprops3( true(size(yourImage)) ,yourImage, 'WeightedCentroid')

12 hours ago | 1

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Detect circles in an image
Use ObjectPolarity='dark'.

19 hours ago | 0

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How to find the volume of a region in a segmented image?
stats = regionprops3(segmentationMap,'Volume')

21 hours ago | 0

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Determine three model Parameters (least squares?)
lsqcurvefit would be appropriate, https://www.mathworks.com/help/optim/ug/lsqcurvefit.html

21 hours ago | 0

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Non linear fit of multiple data set
Because of the constraints, I think you'll just have to do it by Monte Carlo simulation...

21 hours ago | 0

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TD convolution versus FD multiplication
Remember, linear convolution is not the same as cyclic convolution. Make sure you do appropriate zero padding, e.g., x=rand(1,5...

24 hours ago | 0

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How to take cross product of two 2D vector fields
result(:,:,3)=Ax.*By-Ay.*Bx;

1 day ago | 0

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How to find shortest path length by adjacency matrix?
Use the adjacency matrix A to create a graph object, and then use the distances() command. https://www.mathworks.com/help/matla...

2 days ago | 0

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Create single columns of elementwise means
DF=mean(X_dark ,2); FF=mean(X_flat ,2); X_corrected=(X_proj-DF)./(FF-DF);

2 days ago | 0

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How to convert a matrix into some cells?
You can use mat2tiles, which you must Download. A=[1 0 ; 23 13; 1 9; 4 6; 7 13; 0 32]; Acell = m...

2 days ago | 0

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Answered
Put formula into quadprog
That would be, A=[]; b=[]; Aeq=[]; beq=[]; lb=zeros(1,numel(z)); and,

2 days ago | 0

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Answered
Solving system non-linear equations
You could do a numerical grid search using ndgrid to see where if anywhere, the approximate roots lie within a broad set of boun...

2 days ago | 0

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Answered
Generating adjacency matrix for following network
Perhaps as follows, n=6; T=nan(n,2); map=isnan(T); while any(map(:)) [i,~]=find(map,1); if ~map(i...

3 days ago | 0

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Extending a 2D lattice of points
You can use scatteredInterpolant() or griddata().

4 days ago | 0

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Fmincon - Variable dependent constraints
If you wish, you can download prob2matrices() and use the problem-based framework to help set up the linear constraints. x=opti...

4 days ago | 1

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Tridiagonal Matrix with subdiagonal and main diagonal is also matrix
Here's another way, probably much faster. N=1000; a1=4;b1=-1; A =diag(a1*ones(1,N-1)) + diag(b1*ones(1,N-2),1) + diag(b1...

4 days ago | 0

Answered
Tridiagonal Matrix with subdiagonal and main diagonal is also matrix
So, you want a block Toeplitz matrix? N = 5; A =diag([7 4 4]); B=[8 8 10; 2 5 2; 10 8 7]; C=zeros(3); blocks={C,B,A}; ...

4 days ago | 0

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Answered
Non-square FFT
There's probably no significant efficiency to be gained if you just want to get rid of half of the frequencies, as in the examp...

4 days ago | 0

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Optimize Function with two sums using fmincon
k = [5,7,11,13]; p = [1:4]; a0 = [pi/10, pi/8, pi/7, pi/5]; weights=(1./k.^4); weights=weights/sum(weights); fun = @(a)...

5 days ago | 0

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Answered
Add missing numbers between elements in an array
Var1= [1 1 2 4 5 7 7 7 8 10 11 13 14 14 17 17 17 17 18 20]; Var2= [0.5 0.3 0.1 0.6 0.2 0.4 0.8 0.9 0.3 0.2 0.1 0.4 0.8 0.7 0.5 ...

5 days ago | 0

Answered
User defined function that evaluates anonymous function with variable number of inputs
The code would be a lot more efficient and tidy if you had the anonymous function accept an MxN array X. fun=@(X) X*[2,-1,-3,+9...

5 days ago | 0

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Problem is unbounded with linprog
Another way to verify that there is no solution is to look at the dual linear program. min. 8*u+4*v s.t. 2*u +2*v >= ...

5 days ago | 0

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How to color grids underneath a curve and also gradient the grids depending on how much is within curve?
One way, xCenter = 10; yCenter = 10; radius = 10; theta = linspace(180, 270, 50); x = radius * cosd(theta) + xCenter; y = ...

5 days ago | 0

Answered
Can I speed up this matrix multiplication?
For example, the size of Q is 1000x1000, but its rank is 10. If so, then we can decompose Q into a short sum where and are t...

6 days ago | 1

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Question

Malwarebytes thinks these Matlab files are malware
Malwarebytes flagged the 4 files below from my R2020b installation. Has anyone else experienced this? Can I safely assume it's a...

6 days ago | 1 answer | 1

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Answered
sum of kronecker products(four loops)
For me, the following test for N=20 gives a very low percent error, so I would bet that the two are equivalent. N=20; [var1,va...

6 days ago | 0

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Version MATLAB 2020b: How can i convert an array to cell array with specific size?
output=mat2cell(MP1,1,Set)

6 days ago | 0

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Answered
How can the data point, where values start to increase for the first time in a data, be found, as this increase continues at the following 30 values?
This uses the File Exchange contributions groupTrue and groupFcn (Download): G=groupTrue( diff(data)>0 ); g=find( groupFcn(...

6 days ago | 0

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Answered
Select a specific column from a 4-D array
x(1,:,1,1)

6 days ago | 0

Answered
Calculate perimeter of a shape using x,y coordinates input to an array
pgon=polyshape(dataX,dataY); perimeter(pgon)

7 days ago | 0