Matt J

Last seen: Today

6,738 total contributions since 2009

Professional Interests: medical image processing, optimization algorithms

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Answered
spline with non monotonic axis
t = 0:100; x= sin(0.2*t); y = cos(0.6*t); tq = 0:.25:100; xy = spline(t,[x...

7 hours ago | 0

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Usage of structure as input of a function. Is it efficient ?
The thing is that if I stop using structures, I'll have gigantic function calls to write. And if I stop using functions, I'll ha...

1 day ago | 2

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How do I assign values from 1D arrays to 4D arrays efficiently
I do this so I can use vectorization to greatly speed up the performance of my calculations by using element-wise operations. Ho...

2 days ago | 1

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Answered
lsqnonlin is only giving the initial point
I don't know if the solution is what you were expecting, but this gives exitflag 1, la=[39.873297 39.872124 39.869953 39.864596...

2 days ago | 1

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Answered
Find the Argmin of a vector
You should have avoided naming the variables that way, and should have used (for example) a cell array. Indeed. Here's an examp...

3 days ago | 0

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Answered
Recover matrix Z from XZX', Z es symmetric and n-by-n, while X is k-by-n where n>>k
In the case where k truly is <<n, you can use my KronProd class to get the minimum norm solution https://www.mathworks.com/matl...

3 days ago | 0

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Sum of m- fold convolution
if you write the expression in the frequency domain, it just becomes a big polynomial...

3 days ago | 0

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Why is memory reduced for an identical copy of a sparse array?
Are you sure you have to worry about it? According to what I'm seeing (in R2019a,R2020a), the extra 16 bytes occurs only anomolo...

4 days ago | 0

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standard deviation and mean across specific columns of a 3D matrix
If the idea is to average along rows 2 through 5 in every slice, you would want this, MmtxT1 = mean( mtx([2 3 4 5],:,:) , 2); ...

4 days ago | 0

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Answered
How to increase memory available for arrays?
A simple solution might be to close other applications that might be consuming RAM. For example, closing Microsoft Outlook freed...

4 days ago | 0

Question

EVALIN cannot execute a return?
I am trying to create a function that aborts whatever mfile is currently executing after issuing a warning. I see no way of avoi...

4 days ago | 2 answers | 0

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answers

Answered
make vectors same length
One way, collection = {acc,gyr,mag}; minlen = min(cellfun('length',collection)); clipped=cellfun(@(z)z(1:minlen),collecti...

5 days ago | 1

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Answered
Can I change degrees to radians by simply changing from sind to sin?
cos and sin will assume the input angles are measured in radians. If theta is in degrees, you must convert to radians in order t...

5 days ago | 1

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Answered
How to use linear and quadratic programming to optimize w to solve the following problem
This looks like a direct application of lsqlin https://www.mathworks.com/help/optim/ug/lsqlin.html

5 days ago | 0

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count number of indices
Using group1s from the File Exchange https://www.mathworks.com/matlabcentral/fileexchange/78008-group1s col2=arrayA(:,2); I...

5 days ago | 0

Submitted

Extract linearly independent subset of matrix columns
Loop-free code routine to find a maximal subset of linearly independent columns in a matrix

6 days ago | 4 downloads |

Answered
How do I partition a n by m matrix into equal rows
Hint: Consider repelem https://www.mathworks.com/help/matlab/ref/repelem.html

7 days ago | 0

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Integral calculation using matlab
My difficulty stems from the absolute value which is "outside" of the integral Why is this a difficulty? Because it prevents yo...

7 days ago | 0

Answered
finite difference step size value in fmincon
You might try the sqp or interior point algorithm, instead of whatever fmincon algorithm setting you are currently using. Accord...

8 days ago | 0

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Answered
fmincon output is converging to infeasible point
It appears that you are simply trying to find a point where getCost(Y) returns zero. If so, it might make it easier on the algor...

8 days ago | 0

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Algorithm to extract linearly dependent columns in a matrix
See this FEX contribution https://www.mathworks.com/matlabcentral/fileexchange/77437-extract-linearly-independent-subset-of-mat...

8 days ago | 2

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fminbnd loop leads to same optimizer
In addition to hwat John said, you could plot the function to confirm whether fminbnd is giving you a good approximation of the ...

8 days ago | 0

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Answered
return a single vector after a for loop and not individual results
For a fully vectorized solution: [maxval,place]=max(Divergence<=5,[],2); place(maxval==0)=nan; Or, to do the same with a loop...

9 days ago | 0

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Answered
Index in position 1 exceeds array bounds (must not exceed 1). FMINCON
Make theta0 a column vector: >> theta0 = [2,0.2,0.1,0.4].' theta0 = 2.0000 0.2000 0.1000 0.4000

9 days ago | 0

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How can I determine the amount of times a certain value can be achieved by summing values in a matrix?
Below is a more advanced version of my original answer, which is showing greater empirical succes. It incorporates initializatio...

10 days ago | 0

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How to logically index multiple indices while indexing other indices normally?
You probably won't notice much difference with such small data sizes, but reshape is slightly better than permute because it wil...

10 days ago | 0

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Answered
How do I get every combination of 3 vectors?
Example: [X,Y,Z]=ndgrid(1:3,10:15,100:102); [X(:),Y(:),Z(:)]

10 days ago | 1

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Particularly strange bug using the eval function
I also know that MATHWORKS would prefer me not to define variables that clash with their own builtins. However, the code st...

10 days ago | 2

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Can one set up initial values for fminbnd?
No, you cannot. However, you might get a comparable effect if you use fminsearch instead, setting your objective to Inf outside ...

10 days ago | 0

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Answered
Given a point, locate 3 point in different 8 directions.
Or maybe this is what you want. In the code below, A is your image and the result Neighbors(i,j,:) contains all 9 neighbors of A...

10 days ago | 0