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# Matt J

##### Last seen: Today
6.535 total contributions since 2009

Professional Interests: medical image processing, optimization algorithms

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How to make specific elements of a matrix zero before nth element?
[m,n]=size(A); C=A.*((1:m).'>=B);

alrededor de 7 horas ago | 2

Trouble with struct indexing?
... to access a single element of field2. The layout of your struct variable is not clear. If, for example, you have a scalar s...

alrededor de 7 horas ago | 0

Union() operation adds hole to polyshape

alrededor de 10 horas ago | 0

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Approximate a log curve as linear to predict a value
idx=(P<=0.1); c=polyfit(log10(P(idx)),Q_p_1(idx),1); semilogx(P, Q_p_1, P,polyval(c,log10(P)),'x-' )

4 días ago | 0

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3D Array Rastering
I'm not sure from your description how this should generalize for different N, but perhaps this is what you want: >> N=2; Array...

4 días ago | 0

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Using fminsearch I want to plot the model function whose parameters I'm fitting at each iteration without the figure window stealing focus. How do I do this?
Stop invoking whatever command it is (figure(), axes() ?) that you are using to bring the figure into focus. Calling the plot co...

5 días ago | 0

Updating for loop boundaries in MATLAB
for i = 1:size(A,1)

5 días ago | 1

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Calculation of the gradient of a function in BFGS Quasi-Newton Algorithm
With respect to all the variables that are unknown.

5 días ago | 0

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matrix dimensions must agree error
Possibly a missing comma here, K=1/h^2*(2.*diag(ones(1,N+1))-diag(ones(1,N)-1)-diag(ones(1,N),1)); ...

8 días ago | 0

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Define a variable without assigning a value
Perhaps you are trying to do symbolic computations, https://www.mathworks.com/help/symbolic/performing-symbolic-computations.ht...

8 días ago | 0

Submitted

N-dimensional sparse arrays
Creates an N-dimensional sparse array object, for arbitrary N.

How can I use 'Least Squares Solver and Jacobian' instead of 'fminunc'?
Assuming D_d is the Jacobian of myfun, it would be, while (sum(abs(beta_u-beta_d))>0.1 && counter< 500) initial_gues...

9 días ago | 0

How to view centers on a 3D image
One suggestion is to use this FEX file to display the 3D volume with high transparency https://www.mathworks.com/matlabcentral/...

11 días ago | 0

Comparing the performance of colon, loop, and cell indexing
I checked that it is indeed the case with the Run & Time feature. I don't know what that is, but the better test in any case i...

12 días ago | 2

Using 'fminunc', I receive Optimization completed because the size of the gradient is less than the value of the optimality tolerance.
If the problem doesn't have a solution satisfying the tolerance condition in your while loop (sum(abs(beta_u-beta_d))<0.1) the...

12 días ago | 0

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Join table with different lengths
innerjoin(Grouped_Weight_position{i},Country)

12 días ago | 1

Replace array elements with another small array using indexing
b=strrep( strrep(a,[1 4 1],3) ,[3 4 1],2)

14 días ago | 0

Split values in an cell array by using a threshold
One way, A_lower = cellfun(@(x) x(x<threshold), A, 'uni',0); A_upper = cellfun(@(x) x(x>threshold), A, 'uni',0);

14 días ago | 0

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How to solve this equation z = c sqrt(x) ?
c=z/sqrt(x)

14 días ago | 0

Too many output argument error while using nested functions?
The code you've posted does not make it clear what problem you are encountering. There doesn't appear to be anything wrong in th...

14 días ago | 1

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How to multiply a scalar with matrix within loop and for each iteration store the values in new matrix?
There is no need for a loop: C=A.*reshape(b.^(0:n-1),1,1,[]);

14 días ago | 1

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Function lsqnonlin() has no optimization effect
And I have another question. My code has no optimization effect In this case, your initial guess already is optimal. You can se...

15 días ago | 0

Linear Extrapolation with interp2
The only remedy I can think of is to pre-pad the edges of the data V with linearly extrapolated values at distant X, Y. That way...

16 días ago | 0

overlaps() with only two polyshap objects
Use the two-argument form, Obstacles=[obstacle3 obstacle2]; criterion = sum( overlaps(car,Obstacles) ) == 1 ; %true if one a...

17 días ago | 0

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Constraints on meshgrid. Remove points outside function
Just apply logical indexing on the appropriate region and set it to NaN, bad=(y<s11(s2)) | (y>s12(s2)); z(bad)=nan;

17 días ago | 0

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How to run a curve approximation on a script using a function defined in a file and display the goodness of fit in a command window
You can't use the curve fit tool for a curve defined in an mfile. You can use lsqcurvefit, if you have the optimization toolbox,...

17 días ago | 0

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Parallel Processing with Multipul GPUs - fftn
You can use gpuDevice() to select different GPUs for different calculations. gpuArray commands run asynchronously without blocki...

18 días ago | 0

optimization based upon another optimization
You can write anything you want inside the code for your objective function, including other optimization processes. However, fm...

19 días ago | 0

Question

Finding handles to figure text
I am attempting to use findobj to retrieve text objects in a plot. For some reason, this fails (R2018a,b). In the following exam...

19 días ago | 1 answer | 0