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James Tursa


Last seen: 2 days ago 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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Answered
an ode with arguements
Create a new function handle with your extra stuff. E.g., mufunT = @(eta,f) mufun(eta,f,guessT) [eta, f] = ode45(mufunT, [lins...

6 days ago | 0

Answered
Column to matix In matlab
Depends on how your data is currently stored. Suppose the data is currently in a vector v. Then matrix = reshape(v,50,10).'

6 days ago | 0

Answered
How do I process a string class in a mex function?
Strings are opaque objects (like classdef) and there are no API functions to get pointer access to the data areas. I am unaware...

6 days ago | 0

Answered
How to convert dates into Julian dates?
Based on your comment that you are expecting numbers in the range of 273,287,298, etc., if what you are after is actually "day ...

7 days ago | 0

Answered
How to create for loop for calculating euclidean distance of a matrix?
Does pdist() do what you want: https://www.mathworks.com/help/stats/pdist.html?s_tid=doc_ta

12 days ago | 0

Answered
converting 3d matrix into a cell array
x = rand(1001,259,259); result = arrayfun(@(k)squeeze(x(k,:,:)),1:size(x,1),'uni',false); size(result) size(result{1}) But, ...

24 days ago | 0

Answered
How to implement the Central Difference method integrator for a two body problem?
You have: altitude tangential velocity If you just want the orbital period, you can calculate as follows using the Vis-Viva e...

26 days ago | 0

Answered
Can multiple versions of MATLAB be installed on the same Windows PC using the same license number for code compatibility?"
Multiple MATLAB versions can be installed on the same machine as long as your license permits it. Both can even be run simultan...

26 days ago | 0

Answered
How to calculate the angle between two 3D vectors?
See a discussion here (includes a tiny angle example): https://www.mathworks.com/matlabcentral/answers/101590-how-can-i-determi...

1 month ago | 1

Answered
Double precision: Why does fprintf print "extra" wrong non zero digits?
The "extra" digits that look incorrect to you are simply the result of doing an exact conversion of the actual floating point bi...

1 month ago | 1

| accepted

Answered
What does MATLAB actually do when switching precisions?
When converting from IEEE single to double, the sign bit is retained, the exponent bits are adjusted to match the same exponent ...

1 month ago | 2

Answered
I want to solve ODE for a complex systems in a rk4 method
Just turn all the y( ) stuff into row or column vectors. E.g., suppose we use column vectors, then something like this ... y = ...

1 month ago | 0

| accepted

Answered
quat2angle / atan2 strange quadrant change when calculating angle
You don't show us your code, but in general I would note that angle changes like this are sometimes the result of whole quaterni...

1 month ago | 0

Answered
Active rotation with quaternions: from initial orientation given with Euler angles get the new orientation after an active rotation described by the qr quaternion.
Yes, for your convention q' = q * qr is mathematically correct. But note that this formula only works for certain quaternion co...

1 month ago | 1

| accepted

Question


Conjugate of Symbolic Root doesn't change anything
Reference question first asked here: https://stackoverflow.com/questions/78010011/matlab-bug-with-root-and-conj Basically, the...

2 months ago | 1 answer | 1

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answer

Answered
sparse matrix entries are not displayed correctly
I finally finished my sparse matrix integrity checker. You can find it in the FEX under the name SAREK (I think you will be able...

3 months ago | 0

Answered
the tranpose of transpose doed not equals the original matrix
I finally finished my sparse matrix integrity checker. You can find it in the FEX under the name SAREK (I think you will be able...

3 months ago | 2

Submitted


SAREK - Sparse Analyzer Real Et Komplex
The SAREK function analyzes a sparse matrix for integrity. Useful especially for checking sparse matrices built by 3rd party s/w...

3 months ago | 5 downloads |

Answered
Help with state representation of my 3-mass 2-spring system
The k terms in the equations above appear to be non-linear. Your A matrix doesn't account for the cubic parts.

3 months ago | 0

Answered
Calculate angles correctly between two vectors using the dot product.
Also see this related link for a robust method using atan2 that can recover small angles: https://www.mathworks.com/matlabcentr...

3 months ago | 0

Answered
How can I make memory persistent between calls to a MEX-file in MATLAB?
So, the accepted answer has bugs. Namely: They don't include the header for memcpy They don't check the input argument properl...

3 months ago | 0

Answered
Index in position 1 exceeds array bounds (must not exceed 8).
Here is how to debug these types of errors: Type the following at the command prompt: dbstop if error Then run your code. Whe...

4 months ago | 0

Answered
matlab mex in-place editing via "mxUnshareArray" or similar functionality
So, MATLAB has never officially supported modifying input variables in-place in a mex routine. There are potential side effects ...

4 months ago | 0

Answered
Static methods are unnecessary, right?
I use Constant Properties and Static Methods all the time in classes I am creating. In particular, when I am developing a group...

4 months ago | 1

Answered
Speed of the abs function
Although I applaud your thinking about this problem, this level of optimization is hard to achieve with a language such as MATLA...

4 months ago | 2

| accepted

Answered
How would I write these in MATLAB
Depends on what those subscripts mean. E.g., maybe this y41 = -(x41^1.5 * cos(x41)^3) + 40; y42 = x42 * sin(x42^2); or this ...

5 months ago | 0

| accepted

Answered
How to find roots of a quartic function with unknown constant coefficients?
You can look here: https://en.wikipedia.org/wiki/Quartic_function But the nature of the roots is going to depend on the value ...

5 months ago | 0

Answered
What calendar system does MATLAB use?
I know this is an old post, but the accepted answer is a bit misleading. MATLAB certainly does use a specific calendar system. ...

5 months ago | 3

Answered
Rungekuttan for a system of 2 DOE functions
It would be better to have a single state vector for your solution so that you can easily compare your results to MATLAB ode45( ...

5 months ago | 0

Answered
How much data does an array take?
The data is held in contiguous memory, so yes for a full real double an NxN matrix would take 8*N^2 bytes for the data. Then the...

5 months ago | 0

| accepted

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