Matt J
Professional Interests: medical image processing, optimization algorithms
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Content Feed
How to set a custom equation to fit 5 points in space by fitsurface?
I can't find "fitsurface" in the Mathworks documentation, but the fit is easy enough to do algebraically. x=x(:); y=y(:); z=z(:...
ungefär 2 timmar ago | 0
Why is x(:) so much slower than reshape(x,N,1) with complex arrays?
The following simple test seems to support @Bruno Luong's conjecture that (:) results in data copying. The data of B1 resulting ...
ungefär 6 timmar ago | 0
Is it possible to correctly perform a multi-dimensional FFT on a 1D linearised version of a 3D array?
Reshaping to and from 3D format should not add significant cost: Nx = 256; Ny = 256; Nz = 128; N = Nx*Ny*Nz; A0 = rand(N,1)...
ungefär 19 timmar ago | 0
| accepted
Question
Why is x(:) so much slower than reshape(x,N,1) with complex arrays?
The two for loops below differ only in the flattening operation used to obtain A_1D . Why is the run time so much worse with A_3...
ungefär 20 timmar ago | 3 answers | 0
3
answerssee the 3d image and see the coordinates while moving the mouse over the image
You can use imshow() to display any particular slice of the image and then use the axis datatip button to get the in-slice 2D co...
2 dagar ago | 0
How do i find the coordinates of a boundary
How about simply, [m,n]=size(Image); I=boundary(:,1); J=boundary(:,2); corner1 = [1, max(J(I==1))]; %row/column coordinat...
2 dagar ago | 0
How to Draw an ellipsoid between two 3d coordinates
Another way would be to use the ellipsoidalFit.groundTruth method in this File Exchange submission. https://www.mathworks.com/m...
2 dagar ago | 0
Trying to count the number of pixels in an image over a specific RBG value
results.area=nnz(imstd>90);
2 dagar ago | 0
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Normally distributed random numbers with fixed sum
Why not simply, x(1:N-1)=randn(1,N-1); x(N)=fixedValue-sum(x(1:N-1))
2 dagar ago | 0
Only analyze what is outlined in black in an image
If you have a binary mask of the circles, you can just do numBlack = nnz( circles & ~BW ); numWhite = nnz( circles & BW);
2 dagar ago | 0
If the quadprog problem is infeasible, how i can solve it with a certain tolerance?
It never really makes sense to have more equality constraints (here 36) than you do unknowns ( here 6). In order for the problem...
4 dagar ago | 0
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How to construct a "ones" matrix with zero blocks in the diagonal
repelem(1-eye(4),4,4)
5 dagar ago | 1
Iterative solution of non-linear equation with a provided guess value?
You could use fzero's OutputFcn option https://www.mathworks.com/help/optim/ug/fzero.html#btn3z5s-options to access the sequen...
5 dagar ago | 0
Iterative solution of non-linear equation with a provided guess value?
Using fsolve() instead of fzero(), you could solve the problem as a system of two equations in two unknowns. The two unknowns ar...
5 dagar ago | 0
Failure in initial user-supplied nonlinear constraint function evaluation
One problem: nonlcon = @simple_constraint; There is no function called 'simple_constraint' in your attached script. There is a...
5 dagar ago | 1
| accepted
for loop for permutations of for length of array
List=nchoosek([a,b,c],2); for i=1:size(List,1) p1=List(i,1); p2=List(i,2); ... end
6 dagar ago | 1
| accepted
How do I use an if-else structure inside a for loop to investigate if each component of a row vector is inside or outside the boundaries?
Hint: for i=1:numel(vec) v=vec(i); end
6 dagar ago | 0
2*2 Matrix factorization/decomposition
I also found out what I wanted may have something to do with PLU(permuted lower upper decomposition), but am clueless to how to ...
6 dagar ago | 0
How can I call a script within a for loop, looping over multiple files?
result = scriptname(ID{nSubject},Visit{nVisit});
7 dagar ago | 0
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I am trying to find the exact distance of a curvy line.
Why not as follows? I2 = imread('image.jpeg'); blue=bwareafilt( I2(:,:,1)<=50 & I2(:,:,2)<=50 & I2(:,:,3)>=200, 1); Len...
7 dagar ago | 0
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Number of branches per branch point
Perhaps as follows: k=ones(3); k(5)=0; neighborCount=conv2(double(BW),k,'same'); neighborCount=neighborCount.*(neighborCo...
7 dagar ago | 0
| accepted
Rank deficient error.
Are you attempting to do matrix division? if not use ./ instead.
7 dagar ago | 1
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Merge struct with matrix
You cannot avoid a for-loop altogether, but you can avoid writing your own for-loop as follows: tmp=num2cell(modelOutputSignal,...
7 dagar ago | 0
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Unable to detect Iris boundary using imfind circles
Increasing the lower radius bound as suggested by @Jonas as well as increasing the sensitivity setting seems to help: A=any( im...
7 dagar ago | 0
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adjusting the code from optimization output from minimum to maximum
fun=str2func(FUNCTION_NAME); fun=@(x) -fun(x); [Scaled_x_Single,fval,exitflag,output,population,scores] = ga(,3,[],[],[],[],...
8 dagar ago | 0
Question
Re-import a binary map into Image Segmenter or Color Thresholder
I have generated a binary mask of an image using the Image Segmenter app. I am wondering if it is possible to re-import that mas...
8 dagar ago | 1 answer | 0
1
answerFind elements from a submatrix in the main 3D matrix
[row,col]=find( reshape( ismember(M(:),A(:)) , size(M) ) );
8 dagar ago | 1
| accepted
How to smooth data to a negative curve
Thie File Exchange submission allows you to do spline smoothing with monotonicity constraints: https://www.mathworks.com/matlab...
8 dagar ago | 0
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Create new field on struct from names on existing field
names={Stimuli.names}; idxBlue=contains(names,["H1" "H2" "H3"]); idxRed =contains(names,["H4" "H5" "H6"]); [Stimuli(idxBlue...
8 dagar ago | 0
| accepted
How to guide bwconncomp to specific region of image?
If you have a binary circleMask of the circular region, you can use bwlmaskpropfiltn (Download) to eliminate all objects in a la...
9 dagar ago | 0
