James Tursa

Last seen: Today | Active since 2007

Interested in external applications, mex & engine applications with Fortran, C, C++, etc, particularly in the areas of speed improvement and memory management efficiencies.

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transposing 3d matrix with permute function
MATLAB does not store trailing singleton (1) dimensions beyond the 2nd dimension. Once you permute that 1 into the 3rd dimension...

15 hours ago | 2

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Scalar structure required for this assignment.
This? [Sis.On] = D_{:,2};

16 hours ago | 0

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LU decomposition algorithm change
For this particular example: A=[ 1 2 3; 4 5 6; 7 8 9; 10 11 12]; I get two different results depending on...

22 hours ago | 2 answers | 0

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Inserting a double to a cell
E.g., x = randi(100,10,10) % sample data columns = [4,7]; % columns to check minx = min(x(:,columns)) % minimum of the two co...

23 hours ago | 0

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Answered
Using Matlab to solve 1D Schrödinger Equation (Strange Eigenfunctions)
Python: return is misspelled retrun The mL2V( ) function returns 1000*(y-1/2)**2 I don't see where y is defined prior to the ...

2 days ago | 0

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1×0 empty double row vector using find
Welcome to the world of floating point arithmetic. For your specific example, they are not equal. E.g., x=[0 0.1 0.2 0.3 0.4 0....

3 days ago | 1

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How to plot the first derivative of solution?
After the ode45( ) call, simply pass your x solution through your derivative function to obtain the xdot values. You can either ...

4 days ago | 0

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optimizing: fastest way to detect if ANY points are within distance N of points?
Here is a naive brute force mex routine you can try out. It makes no attempts at cache optimization or multi-threading, and is p...

10 days ago | 0

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"roots" call is not providing the correct answer
Rename your old roots file (preferred method) or move it to a directory that is not on the MATLAB path. That way it won't shadow...

10 days ago | 1

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How can ı solve this error ??Unable to perform assignment because the size of the left side is 1-by-5 and the size of the right side is 26-by-1.
You could expand the size of the LHS array. E.g., poles_real(i, 1:numel(roots_poly)) = real(roots_poly); poles_imag(i,...

11 days ago | 0

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angle of a vector centered at a certain point
Once you have the vectors, you can calculate the angles between the vectors using the technique I posted here: https://www.math...

11 days ago | 0

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How to expand dimension of a 2D array
All MATLAB trailing singleton (1) dimensions beyond the 2nd dimension are not physically stored, and will not show up in a size(...

11 days ago | 2

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A single precision matrix multiplication problem
Somewhat related side comments: In general, the BLAS/LAPACK libraries do not contain mixed type argument routines. E.g., there ...

15 days ago | 2

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How is this even logical?
When assigning into rows or columns via indexing, MATLAB will conform a RHS vector from row or column to row or column if necess...

24 days ago | 0

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Matlab crashes when running a specific Fortan MEX file under MacOS
The MATLAB Fortran API interface needs to be treated as a pass-by-reference interface. That means you need to have the exact typ...

26 days ago | 0

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What does [n==0] means?
Try it out and see: n = 3; N = 3; n == 0 n == N n = randi(4,1,10) - 1 n == 0 n == N Returns logical true/false where val...

30 days ago | 0

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How to update a symmetric matrix?
E.g., M = rand(6)<0.3; M = double(logical(M+M')) % an arbitrary symmetric matrix VarMin= 1; % Lower Bound of Variables...

1 month ago | 0

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Recursive Method returning answers backwards
This is a very convoluted way to program the Euler method. There is no need for recursion here, just use simple loops instead. ...

1 month ago | 1

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How to randomize order of functions
E.g., Using the cell array approach with randperm: function [results] = runTests(testparameters) f = {@test1,@test2,@test3,@te...

1 month ago | 0

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Answered
eval() is too slow to numerically evaluate a function with X(t) and Y(t).
Something like this? syms X(t) Y(t) Vfun = [2*X + Y ; cos(X)*X^2 + Y^3 ; 3 + sin(Y)] syms x y vfun = subs(Vfun,[X Y],[x y])...

1 month ago | 0

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Answered
I have one column data 57600 points, how can i convert it to 240 by 240 matrix!
x = your column vector result = reshape(x,240,240); or you might need the transpose: result = reshape(x,240,240).';

2 months ago | 0

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I want to calculate pi^2 to 22 decimal places
You can use this excellent FEX submission by John D'Errico: https://www.mathworks.com/matlabcentral/fileexchange/36534-hpf-a-bi...

2 months ago | 2

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How to stop running code once conditions are met?
If your Birthday function is supposed to represent only one trial (a reasonable thing to do), then you should be returning n, no...

2 months ago | 0

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How to fix the must be a column vector error?
You should double check your derivative function. Shouldn't the result be a 4-element column vector that is a function of q? Ne...

2 months ago | 0

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How to compare elements of two vectors in MATLAB ?
Compare for what purpose? E.g., these statements will compare them: isequal(v1,v2) % are they equal v1 == v2 % matrix of indi...

2 months ago | 0

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Problem with time steps in Runge-Kutte method
"... I get different results with different time steps ..." In general, that is the expected result. I suppose the real questi...

2 months ago | 1

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angle2dcm: How to reference direction cosine matrix output?
Does this do what you want: x = zeros(1,m); % reorder these to row vectors y = zeros(1,m); z = zeros(1,m); : xyz = [x;y;z];...

2 months ago | 0

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Answered
Motion equation of a space engin in low earth orbit
As Bjorn has pointed out, your J2 terms are all the same but they should be different because the equatorial bulge affects the z...

2 months ago | 1

Answered
Problem using 4th order Runge-Kutta method
You have a factor of 2*K4 that shouldn't be there. It should just be K4. E.g., Fx = @(t,x,vx,y,vy,z,vz) [vx; 3*t; vy; t; vz; 7*...

2 months ago | 0

Answered
How can I find angle between two vectors in 3D ranging from 0 to 360 or -180 to +180?
https://www.mathworks.com/matlabcentral/answers/501449-angle-betwen-two-3d-vectors-in-the-range-0-360-degree

2 months ago | 0

James Tursa

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