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James Tursa


Last seen: 1 day 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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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...

11 days 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...

1 month 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...

1 month 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...

1 month 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.

2 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...

2 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...

2 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...

2 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 ...

3 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...

3 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...

3 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 ...

3 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 ...

3 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. ...

4 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( ...

4 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...

4 months ago | 0

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Answered
Multiply matrices in cell array by another matrix
You may be stuck with the loop. There are ways to rearrange and stack things so that you can do everything in a single matrix m...

4 months ago | 0

Answered
Reading a large binary file
Try data = fread(fd, '*int16'); When you use 'int16' for the type to read, MATLAB reads as int16 and then converts to double (...

5 months ago | 1

| accepted

Answered
Incorrect Dimensions for matrix multiplication
Because you are using matrix operators instead of element-wise operators. Try this: Rtf=(cosh(m.*Lf)+(h./(m.*Kf)).*sinh(m.*Lf))...

5 months ago | 0

Answered
Why is pow2() slow? Fastest way?
Another way is just to add d to the exponent bits. Probably fastest to do this in a mex routine where edge checking can easily b...

5 months ago | 0

Answered
Values are getting converted to double automatically.
Here is what I get just displaying the character string. I inserted brackets [ ] for concatenation: ab=[0.5,0.75,1,1.25,1.5,2];...

5 months ago | 2

Answered
help with parallelization of matrix operations
Both of these operations can be multi-threaded in the background, but this kind of timing test is not straightforward to do beca...

5 months ago | 0

Answered
Field II kidney example does not work due to "Requested array exceeds the maximum possible variable size." error
At first glance this is the obvious problem in the original source code: The dimensions array needs to be the proper integer si...

5 months ago | 0

| accepted

Question


Is there a classdef startup/initializer method?
When a classdef is first loaded into memory (via object instance creation or static method call etc.), is there a way to get a s...

6 months ago | 1 answer | 1

1

answer

Question


How to update leap seconds
The current version of MATLAB has a function to give you the leap second information that it is using. E.g., [T,vers] = leapsec...

6 months ago | 2 answers | 0

2

answers

Answered
A MEX solution to split classdef-defined object arrays into cells
You need to use mxGetProperty( ) to get at the properties of a classdef object. And since this returns a deep copy, no need for ...

6 months ago | 1

| accepted

Answered
Why does accessing a multi-dimensional array with fewer indices than its total dimensions not result in an error in MATLAB R2022b?
The accepted answer is misleading. When you access a multi-dimensional array with fewer indexes than its total dimensions, MATLA...

6 months ago | 3

Answered
Create Mex files for Matlab, from .FOR files of Fortran
So, I haven't had access to a Fortran compiler in over 10 years. And as a result I haven't been maintaining any of my Fortran F...

7 months ago | 0

Answered
Unusal error "Current use of the variable is inconsistent with its previous use or definition".
See how the +b is purple? That means MATLAB thinks you are invoking a as a function with +b as a character string input. Hence ...

7 months ago | 1

| accepted

Question


Incorrect datetime UTCLeapSeconds conversion
I am working with leap second data, and as part of the calculations I did this for a particular leap second: dt1 = datetime(197...

7 months ago | 1 answer | 0

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answer

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