# Matt J

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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**Content Feed**

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

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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I meet a formula about bilinear interpoltaion, but it not mention the 'int' in formula, how can I convert it to matlab code?

You could just use interp2.

6 hours ago | 0

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

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

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

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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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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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

Plotting graph for specific columns and rows

plot(yourTable{1:4000,20}, yourTable{1:4000,60})

4 days ago | 0

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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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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

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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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

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

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

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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answerHow 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

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

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

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

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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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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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

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

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

How to remove thin lines from the following image?

Perhaps bwpropfilt(bW,'Eccentricity',____)

7 days ago | 0

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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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