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Matt J


Last seen: Today Active since 2009

Professional Interests: medical image processing, optimization algorithms

PLEASE NOTE: I do not read email sent through my author page. Please post questions about FEX submissions in their respective Comments section.

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Answered
Finding the vertical offset of a gaussian fit
This File Exchange routine does gaussian+constant fitting: https://www.mathworks.com/matlabcentral/fileexchange/69116-gaussfitn...

etwa 2 Stunden ago | 0

Answered
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(:...

etwa 9 Stunden ago | 0

Answered
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 ...

etwa 13 Stunden ago | 0

Answered
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)...

ein Tag 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...

ein Tag ago | 3 answers | 1

3

answers

Answered
see 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 Tage ago | 0

Answered
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 Tage ago | 0

Answered
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 Tage ago | 0

Answered
Trying to count the number of pixels in an image over a specific RBG value
results.area=nnz(imstd>90);

2 Tage ago | 0

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Answered
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 Tage ago | 0

Answered
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 Tage ago | 0

Answered
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 Tage ago | 0

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Answered
How to construct a "ones" matrix with zero blocks in the diagonal
repelem(1-eye(4),4,4)

5 Tage ago | 1

Answered
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 Tage ago | 0

Answered
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 Tage ago | 0

Answered
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 Tage ago | 1

| accepted

Answered
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 Tage ago | 1

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Answered
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 ...

7 Tage ago | 0

Answered
How can I call a script within a for loop, looping over multiple files?
result = scriptname(ID{nSubject},Visit{nVisit});

7 Tage ago | 0

| accepted

Answered
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 Tage ago | 0

| accepted

Answered
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 Tage ago | 0

| accepted

Answered
Rank deficient error.
Are you attempting to do matrix division? if not use ./ instead.

7 Tage ago | 1

| accepted

Answered
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 Tage ago | 0

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Answered
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...

8 Tage ago | 0

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Answered
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 Tage 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 Tage ago | 1 answer | 0

1

answer

Answered
Find elements from a submatrix in the main 3D matrix
[row,col]=find( reshape( ismember(M(:),A(:)) , size(M) ) );

8 Tage ago | 1

| accepted

Answered
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 Tage ago | 0

| accepted

Answered
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 Tage ago | 0

| accepted

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