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James Tursa


Last seen: 23 giorni 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
How to get the ceofficients of a expression derived by ODE or integral ? For exampli,C1 and C2 in u
Typically these would be obtained by combining the solution with initial values for u. Do you have initial values?

24 giorni ago | 0

Answered
Conversion Wolfram Mathematica to Matlab (Do loop)
result = sum(1:100);

26 giorni ago | 0

Answered
Is it possible to vectorize this 'for loop' involving multiple matrix inversions
You might look at this FEX submission by Bruno Luong: https://www.mathworks.com/matlabcentral/fileexchange/24260-multiple-same-...

circa un mese ago | 0

| accepted

Answered
Mulitplying 3D matrix by 3D matrix - result being 4D.
result = pagemtimes(matrix1,reshape(matrix2,3,512,1,512));

circa 2 mesi ago | 0

| accepted

Answered
Matrix dimensions must agree error problem
Use element-wise division with the dot: Y=acosd(sin(altitude)*sin(latitude)-sin(declination)./(cos(altitude)*cos(latitude))); ...

circa 2 mesi ago | 0

Answered
Combining two Matrices every other row
You could do direct assignment. E.g., [m,n] = size(A); C = zeros(2*m,n); C(1:2:end,:) = A; C(2:2:end,:) = B;

circa 2 mesi ago | 0

Answered
Gauss-Elimination method
See the rank( ) function: https://www.mathworks.com/help/matlab/ref/rank.html?s_tid=doc_ta

circa 2 mesi ago | 1

Answered
Looping num2str
x(i) references a single element of x. However, the expression [num2str(y(i)),'%'] generates multiple characters. In essence, ...

circa 2 mesi ago | 1

Answered
Mean computaion in matlab
You can specify the dimension to use with the mean( ) function. E.g., maybe this is the computation you want: data = your 3D m...

circa 2 mesi ago | 0

Answered
What is the mean?
B' is the complex conjugate transpose of B. If B is real, then it is equivalent to just the tranpose and the assignment simply ...

circa 2 mesi ago | 0

| accepted

Answered
How can I model equation of motion (2nd order ODE) when system matrices are in terms of state variables?
Yes you can have derivative functions that depend on state variables. This is quite common. E.g., define a 4x1 state vector y th...

2 mesi ago | 0

Answered
empty double matrix in case of nul value
Do you mean you want to do something like this: if( isempty(malicious) ) malicious = 0; end

2 mesi ago | 0

Answered
To allocate character array='2a'
'2a' is a two element character string. You can't assign two elements to a single element. I.e., you can't assign a 1x2 vector...

2 mesi ago | 0

Answered
How to get the desired quaternion representation from a rotation matrix?
As you already know, both q and -q represent the same rotation. Which sign to pick is entirely up to the underlying algorithm. ...

3 mesi ago | 0

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Answered
Implementation of Runge Kutta Numerical Solution for system of ODE's
The main technical problem (other than your syntax not being MATLAB) is that you are trying to solve your four 1st order equatio...

3 mesi ago | 0

| accepted

Answered
How to convert complex float to complex integer in MEX gateway function?
I would guess you can just use the appropriate data types. E.g., mxComplexInt32* Data1 = mxGetComplexInt32s(prhs[0]); mxComp...

3 mesi ago | 0

| accepted

Answered
Can you help me with this loop?
Can you use num2str? Message = [num2str(TotalMinutes) ' minutes are equal to ' num2str(Hours) ' hours and ' num2str(Minutes) ' ...

3 mesi ago | 0

Answered
How to separate a string(1x1 cell) into a 1x4 cell
If the hex codes are always 8 characters, why can't you just pick off the characters you want? E.g., {result(1:8),result(10:17...

3 mesi ago | 1

Answered
how to generate a code for solving 2st order differential equations using improved runge kutta 4th order method
The posted code actually has a bug. Also it is almost set up properly for vector solutions, but not quite. Make these changes:...

3 mesi ago | 0

Answered
Computer crashed when calculating matrix (mixed with sparse and full) multiplication and summation
Remember that each element of the B*C result is simply the dot product of a row of B with a column of C. If that column of C ha...

3 mesi ago | 0

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Answered
Fast vector reshaping/permutation
Don't do the permute( ) operation. Just use pagemtimes( ) downstream in your code with the appropriate 'transpose' option. Thi...

3 mesi ago | 1

Answered
Can someone explain this Loop?
Of the numbers 1 ... 10 that get produced by the randperm( ) call, only three of them are less than 4: 1, 2, 3. 1 will cause n...

3 mesi ago | 0

| accepted

Answered
How to generate unique random integers between 1 to n (with no possibility of Sequence)
If 1:n is the only sequence you don't want, just use randperm(n) and reject the one case you don't want. I.e., if you get it the...

3 mesi ago | 0

Answered
How do solve four variables with one equation using Runge-kutta?
You have three state variables, namely v, lc, and z. But you only have code for updating v. You need code for updating lc and ...

3 mesi ago | 2

| accepted

Answered
A code and plot a graph for a projectile motion of a ball
Your main problem is that you don't have enough state variables. You have these two equations: x'' = 0 y'' = -g That's two 2...

3 mesi ago | 0

Answered
Converting Struct field to array
Does this do what you want? MyMatrix = vertcat(MyStruct.Field);

3 mesi ago | 0

| accepted

Answered
Trying to build a new nx4 array from an existing nx4 array using logical values
Assuming quatAB is a standard numeric matrix, use your logical variable for the first index and colon for the second index: m =...

3 mesi ago | 0

Answered
How do I combine a structure array into one structure
F = fieldnames(A); n = numel(F); C = arrayfun(@(i)vertcat(A.(F{i})),1:n,'uni',false); FC = [F';C]; B = struct(FC{:});

3 mesi ago | 0

Answered
Finding optimal value for x
You could try this function to get numeric values for local minimums: https://www.mathworks.com/help/matlab/ref/fminsearch.html...

3 mesi ago | 0

Answered
Using fprintf to save a matrix changes the order of my matrix
MATLAB stores 2D matrices in column order. That is, the numbers in your matrix are stored in memory in this order: 0, 1, 2, 3,...

3 mesi ago | 0

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