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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
max value of a function
In general I use: x= double(solve(diff(func))); This assumes there are no local min/max or saddle points. if i try to use max...

1 hour ago | 0

Answered
Fastest way to compute a multiplication of matrices times a sequence of kronecker products
With this FEX package https://www.mathworks.com/matlabcentral/fileexchange/25969-efficient-object-oriented-kronecker-product-ma...

6 hours ago | 0

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Answered
for loop storing the same variable
Because in every pass through the loop, you assign the result to the same location. Perhaps you meant, demodulated_power_vector...

9 hours ago | 0

Answered
Error when using sptensor in parfor
You could try with ndSparse() instead of sptensor() https://www.mathworks.com/matlabcentral/fileexchange/29832-n-dimensional-sp...

3 days ago | 0

Answered
Calculate the mean of nonzero pixels and setting a threshold
fun=@(z) nanmean(z(z<99)); my_mean = accumarray(double(mask(:))+1, my_array(:),[], fun)

3 days ago | 1

Answered
Can I use a nearest neighbor extrapolation strategy with interp1?
If you want to mix interpolation and extrapolation methods, use griddedInterpolant instead: F=griddedInterpolant(1:5,'linear','...

4 days ago | 0

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Answered
Find unique number sets
A = [1 4; 2 3; 3 2; 1 4]; [B,iA]=unique(sort(A,2),'rows')

4 days ago | 0

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Answered
How to find all possible 8x8 submatrices of a 13x8 matrix?
Using this File Exchange tool set, https://www.mathworks.com/matlabcentral/fileexchange/115340-block-transposition-permutation-...

4 days ago | 1

Answered
Plotting graph for specific columns and rows
plot(yourTable{1:4000,20}, yourTable{1:4000,60})

4 days ago | 0

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Answered
Class implementation such that assignment x=MyObj does in fact x=MyObj.prop1
You can't have precisely what you have asked for, but you can do this, classdef TestClass < handle properties pro...

4 days ago | 0

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Answered
How to create a rectangular mask based on current code for making an elliptical mask
You could also just use poly2mask. This would avoid the overhead of imrotate. M=256; N=256; %Image dimensions diamMax=60; ...

4 days ago | 0

Answered
How to create a rectangular mask based on current code for making an elliptical mask
I don't understand how your current code works, but you might consider modifying the code below, as appropriate: M=256; N=256...

4 days ago | 0

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Answered
Backslash does not provided the solution with the smallest 2-norm
In this case, we expect that MATLAB returns the solution x which has the smallest 2-norm, right? No, the backslash operator wil...

4 days ago | 1

Answered
How to resample vectors of different length into the same length?
How can I achieve that? You can use interp1 Also should I resample to the biggest size out of the vectors or bring them all to...

4 days ago | 0

Answered
How find the row number for different elements in a column?
As an example, suppose you wanted to find the first occurrence of a 2 in each column. Then one way would be, A=randi(10,10,5) ...

4 days ago | 0

Answered
Help with DFT Algorithm (No FFT)
When I carry out this calculation I get the following: . No, because 1/3 of your xx are padded zeros. This will reduce your amp...

5 days ago | 2

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Question


Using find() is faster than direct logical indexing?
Does it make sense that using find() instead of direct logical indexing is faster in this example: A=randi(100,5e3,5e3); tim...

5 days ago | 1 answer | 0

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answer

Answered
How to call the row number of an element?
With find, but be mindful that direct logical indexing is often faster if you are seeking to modify the matrix. Compare: %Repla...

5 days ago | 0

Answered
AUC or trapz for irregular shape that intersects itself
Perhaps as follows? p=polyshape(WL_1546La, WL_1546Fa); Areas=area(regions(p))

6 days ago | 0

Answered
Is it possible to loop through and set image pixels with a parfor loop?
If you have the Image Processing Toolbox, you should use imwarp to perform an image transformation.

6 days ago | 1

Answered
Why does filtering data before PCA improve results?
PCA applied to the transformed cluster should find PC1 close to L', and therefore the projections of the images on L' should be ...

6 days ago | 0

Answered
how can I find the max value out of iterative for loop ?
Seems to be working: count=1; while 1 for i=1:20 x(i)= randi(87);% calculations end maxvalue(cou...

7 days ago | 0

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Answered
Store m iterations of a variable in for loop
Perhaps as follows: ivals=1:step:m; J=numel(ivals); [LAT_3,LON_3,ALT_3]=deal(nan(1,J)); for j = 1:J i=ivals...

7 days ago | 0

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Answered
How to generate a smooth derivative after fitting a curve to the data?
You can try some different choices of the smoothing parameter, load Data % using cubic spline pp = spline(x,y); derX= fnde...

7 days ago | 0

Answered
Using structures with Functions
@Stephen23's answer might be what you are looking for, but if you need the struct in scalar form for some reason, then the attac...

7 days ago | 1

Answered
How do I combine 3 figures into a single plot and compare them?
Perhaps this is what you mean. Start with 3 plots, colors={'r','g','m'} for i=1:3 figure(i); h(i)=plot((0:4)+i,colors{i}); y...

7 days ago | 0

Answered
How to remove thin lines from the following image?
Perhaps bwpropfilt(bW,'Eccentricity',____)

7 days ago | 0

Answered
Using bwpropfilt after imrotate
The reason, I suspect, that the number of objects seems to decrease when you imrotate is that you have several objects that are ...

8 days ago | 0

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Answered
how can I solve this problem
Are N and W known variables? Your code does not provide them, but if they are known, you can reorganize as a polynomial and use ...

8 days ago | 1

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