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James Tursa


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3.600 total contributions 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
Preallocating a sparse matrix, then entering values column by column takes too much time. Is there a more efficient way ?
The problem is that every time you change the elements of Q, even if it is only one element change, MATLAB generally has to copy...

1 giorno ago | 0

Answered
How to optimize matrix multiplication speed?
This looks like a covariance matrix update to me. The matrix multiplies are already done by highly optimized multi-threaded com...

2 giorni ago | 0

Answered
How to limit calculation precision?
You can get about that precision (a little less) by using the half data type: https://www.mathworks.com/help/fixedpoint/ref/hal...

5 giorni ago | 1

Answered
FOR LOOP NOT WORKING
Index your answers. E.g., if EXANGLES(i) < 90 EVANGLE1(i) = EVSUB1-FT126; elseif EXANGLES(i) == 90 ...

6 giorni ago | 0

Answered
Numerical Solution of the System of four Coupled Nonlinear ODEs by Runge-Kutta Fourth Order Method
I will point out some problems, and then suggest a much easier way to do this. Start with your first couple of lines in the loo...

6 giorni ago | 0

Answered
can i get mex files in matlab format?
Mex files are compiled (i.e., machine language) DLL files. You cannot view them in MATLAB m-file format. If you have the C/C++...

6 giorni ago | 0

| accepted

Answered
I need help obtaining the values c1,c2.c3 from a least squares fit of the data.
It appears to me that your equation is linear in c1, c2, c3. Just make a matrix equation out of this and then apply your least ...

7 giorni ago | 0

Answered
How to add an NxN matrix with K pages ?
You are correct, sum(A,3) is the correct syntax to use. This sums across the 3rd dimension.

12 giorni ago | 0

Answered
How do I vectorize matrices of specific modes of a tensor?
Is this what you want? x = your 250 x 250 x 183 array result = reshape(x,250*250,183);

14 giorni ago | 0

Answered
Why the memory Limitation to a data structure in cpp: size of "XXX::C_SubNetwork::S_ListBuffer [3]" >= 256 Mb and can I raise the limit higher?
This looks like you are declaring this variable as a local variable, in which case the memory for it will come off of the stack....

15 giorni ago | 0

Answered
mxCreateNumericMatrix and sparse matrix in C/Matlab hybrid programming
Convert the index arrays to double either inside the C code or on the Engine side. E.g., engEvalString(ep, "MS=sparse(double(MI...

18 giorni ago | 0

Answered
Converting double values file to 2 byte per sample.
If you want a two byte floating point representation you can use half precision. E.g., https://www.mathworks.com/matlabcentral/...

20 giorni ago | 0

Answered
How can I multiply N dimensional matrices
Other options from the FEX: https://www.mathworks.com/matlabcentral/fileexchange/8773-multiple-matrix-multiplications-with-arra...

20 giorni ago | 1

Answered
whats difference beetween angvel and rotvec?
I don't have a version of MATLAB installed that has the angvel( ) and rotvec( ) functions, so I can only make an educated guess....

21 giorni ago | 0

Answered
Strncpy/Strncpy_s is supported by Matlab
Your code has bugs. That is why it is crashing. The bugs are caused by these lines: main(); // You call main without any ...

21 giorni ago | 0

Answered
Fast conversion of 2 matrices to 1 complex matrix
See this FEX submission for reading and writing interleaved complex data in R2018a or later without extra data copies: https://...

28 giorni ago | 0

Answered
How to replace leading zeroes by spaces with regexprep
One way: fun = @(x)sprintf(['%' num2str(numel(x)) 'd'],str2double(x)); d = cellfun(fun,a,'uni',false); e = cellfun(fun,b,'uni...

28 giorni ago | 0

Answered
trimming matrix arrays arranged within cell arrays
It is not clear whether you want the rows or columns trimmed. Maybe one of these is what you want? TrimmedArray = cellfun(@(x) ...

28 giorni ago | 0

Answered
Runge-Kutta 4th order function error (Matrix dimensions must agree)
Your RK_4 function is not set up to handle vector equations ... it is only set up to handle scalar equations. Also you are not ...

28 giorni ago | 0

Answered
How to pass arguments by reference from Matlab?
doc loadlibrary Create a C header file that gives prototypes for the Fortran subroutines and treat the Fortran arguments as poi...

circa un mese ago | 0

Answered
how to create an array of all permutations
If you want all of them in an array (which might be too large if the number of digits is too large), you can use n = number of ...

circa un mese ago | 0

| accepted

Answered
Trying to do calculations for density
Why do you have these lines in your function: P_t=4; P_s=3; H=25; Aren't these variable supposed to be input arguments? See...

circa un mese ago | 0

| accepted

Submitted


freadcomplex and fwritecomplex
Mex routines that read and write interleaved complex data files for MATLAB R2018a or later without extra data copy.

circa un mese ago | 3 downloads |

Answered
efficient ways to read and write complex valued data
A mex routine to accomplish this that doesn't use any hacks can be found here: https://www.mathworks.com/matlabcentral/fileexch...

circa un mese ago | 0

| accepted

Answered
efficient ways to read and write complex valued data
This may not apply to you, but if you have R2018a or later you can just fread( ) into a real variable directly the interleaved d...

circa un mese ago | 0

Answered
Changing contents of Cell Array mex files
When you mxDestroyArray a cell array or struct array, it does a deep destroy. Meaning all of the cell array or struct array ele...

circa un mese ago | 0

| accepted

Answered
solution with the Runge-Kutta method HELPP
This is clearly a homework/exam question, so I will only offer hints. The code you have posted is for a single scalar different...

circa un mese ago | 0

Answered
How could I use MATLAB to solve for x with this equation, 0=a*x^(3)+b*x^(-1)+c.
Just use the roots( ) function. If you have a negative integer power of x in the expression such as x^(-n), then multiply every...

circa un mese ago | 0

Answered
reshape loop resulted cell array
result = cell2mat(c1(:))';

circa 2 mesi ago | 0

| accepted

Answered
Matrix with nested for loops
You don't need loops for this. E.g., p = the probability result = rand(20,20) < p; % your matrix of 0's and 1's

circa 2 mesi ago | 0

| accepted

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