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Matt J


6,068 total contributions since 2009

Professional Interests: medical image processing, optimization algorithms

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Answered
Solving large linear system of Ax=b while A is a non-symmetric Matrix?
You could pre-multiply your equation by A.' to obtain the square symmetric system (A.'*A)*x=A.'*b and then use pcg or gmres as...

11 minutes ago | 0

Answered
Edge linking and hole filling in binarized cell image
Use imclose with a disk structuring element se=strel('disk',n); ~imclose(~yourImage,se);

7 hours ago | 0

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fminunc stopped because it cannot decrease the objective function
The log of a sigmoid is a numerically delicate operation. You need to write your objective function with a dedicated log-sigmoid...

9 hours ago | 0

Answered
finding all possible polynomial combinations of n variables
This should be better: n=30; combs=nchoosek(1:n,2); m=size(combs,1); S=sparse([1:m;1:m],combs.',1,m,n); exp_comb = [S;s...

1 day ago | 1

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Answered
finding all possible polynomial combinations of n variables
[vars{1:n}] = ndgrid(0:2); exp_comb = reshape(cat(n+1,vars{:}) ,[],n); exp_comb = exp_comb(sum(exp_comb,2)<=2 & sum(exp_c...

1 day ago | 1

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Coordinates of corners of quadrilateral in binary mask
The Computer Vision Toolbox has some ready-made corner detection functions, e.g., https://www.mathworks.com/help/vision/ref/det...

1 day ago | 0

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Answered
Remove coordiantes with less than n repeats in y coordinate
G=findgroups(y); [C,~,idx]=histcounts(y, 1:max(G)+1); keep=C(idx)>=n; coords=coords(keep,:)

1 day ago | 0

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Answered
Implement average filter without using built-in functions
In all likelihood, you have not converted your image to floating point img = im2double( imread("Q3_Input", "tif") );

2 days ago | 0

Answered
Linear Programming: Can you input fixed values to the output matrix ('x') before solving linprog for 'x'?
You can enforce this using upper and lower bounds ub(i)=lb(i)=knownvalue

2 days ago | 1

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Answered
Sum of matrix times scalars
Hold your 3x3 matrices in a 3x3xN array caled T and your scalars in an Nx1 vector called a and do, result=reshape(T,9,[])*a(:);...

2 days ago | 1

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Answered
Please help me to using genetic algorithm
You can use prob2struct to obtain most of your problem parameters in solver form, problem=prob2struct(costprob); problem=rmf...

2 days ago | 0

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Answered
How to Convert Euler Angles (Z-X-Z Convention) to Axis Angles for Image Stack Rotation
If angle2 is a rotation in y, I think you really meant rot2 = imrotate3(rot1,-angle2,[0 1 0],'crop'); % rot about y

2 days ago | 0

Answered
How to Convert Euler Angles (Z-X-Z Convention) to Axis Angles for Image Stack Rotation
If you're going to use imrotate3 why not obtain rot3 in a single rotation of the dataset? [V,d]=eig(R,'vector'); [~,i]=min(ab...

2 days ago | 0

Answered
Set parameterlimits while fitting with fminsearch
Here is a fairly popular version of fminsearch that lets you apply constraints https://www.mathworks.com/matlabcentral/fileexch...

2 days ago | 0

Answered
Efficient way to assign single vectors to a cell array
for j = 1:length(monthName) filename = [directory, 'series', monthName{j}, '.mat']; S = load...

3 days ago | 0

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Answered
Slicing a matrix into multiple matrices
You can use mat2tiles https://www.mathworks.com/matlabcentral/fileexchange/35085-mat2tiles-divide-array-into-equal-sized-sub-ar...

3 days ago | 0

Answered
Fminsearch to minimize norm of rms vector and thus giving me an optimized A and B matrix
fun=@(X) RMSE(X,Test_C,Test_D,Test_U,Test_t,Test_SV, Surge_field, Heave_field, Pitch_Angle_field, Pitch_Rate_field) X_Min = f...

5 days ago | 0

Answered
Applying a change of variables inside fmincon
You could add a regularizing penalty to better specify the solution p_i in the cases where it is ambiguous. Maybe an L1 penalty ...

5 days ago | 0

Answered
Applying a change of variables inside fmincon
If the dimension R^l is not too large, you could use vert2lcon https://www.mathworks.com/matlabcentral/fileexchange/30892-analy...

5 days ago | 0

Answered
How to check if an entire column of string variables can potentially be converted to numerical values?
all(48<=yourMatrix(:) & yourMatrix(:)<=57)

5 days ago | 0

Answered
Calculating statistical functions for a structure array which each cell has a different size
A structure array doesn't have "cells" and doesn't look like that. I assume you really mean your data is a cell array, in which ...

6 days ago | 0

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Answered
For loop for summation
R= zeros(size(y)); N= -500:500; for j=1:numel(N) n=N(j); R = R + f(n).*y.^(-n); end

6 days ago | 1

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Answered
Superimposing matrices in a specific location
Something like this, perhaps: [i0,j0]=deal(700,850); %target location [I,J,S]=find(smallMatrix); result = largeMatrix + ...

6 days ago | 0

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Answered
Trouble calculating column mean from a matrix - using different indices for each row
[m,n]=size(myMatrix); %Edited e=1:n; mask=VariableIndex1(:)<=e & e<=VariableIndex2(:); result=sum(myMatrix.*mask,2)./sum(...

7 days ago | 0

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Answered
Kron error when dealing with sparse gpuarrays
You may want to look at, https://www.mathworks.com/matlabcentral/fileexchange/25969-efficient-object-oriented-kronecker-product...

7 days ago | 0

Answered
Use several pools of workers in a parfor loop
Your terminology is a bit confusing. There is only ever 1 pool of workers, but each worker may use multiple cores and the entire...

7 days ago | 0

Answered
How to write your own function for infinity-norm of a matrix
To sum the rows of any matrix A, sum(A,2)

7 days ago | 0

Answered
Fastest way to substitute elements in a matrix at given positions?
idx = sub2ind([n,m], repmat((1:n).',1,l) ,B); A(idx)=value;

8 days ago | 0

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