James Tursa

Last seen: Today

4,002 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
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...

7 hours 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...

10 hours ago | 1

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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...

1 day ago | 0

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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...

5 days 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 ...

5 days ago | 1

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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...

5 days ago | 0

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

7 days ago | 0

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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 =...

8 days ago | 0

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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{:});

8 days 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...

8 days ago | 0

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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,...

9 days ago | 0

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please help me to convert c code into matlab code for partial shading of solar panel using equilibration algorithm
In addition to what @Image Analyst has written, I would advise turning this into a function with p1, p2, p3 as input arguments a...

9 days ago | 0

Answered
Difference between using single quotes ('xyz') and double quotes ("xyz") in formatspec
In MATLAB, single quotes ' ' are used to create char type variables, and double quotes " " are used to create string type variab...

15 days ago | 0

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Answered
Error in ode45 while doing numerical integration
The function handle you pass to ode45( ) needs to have a (t,y) signature. E.g., [t,y] = ode45(@(t,y) myode(t,gt,g), tspan, ic, ...

15 days ago | 0

Answered
How to multiply higher order matrices?
You may need to permute your arrays first to get your desired 2D slices in the first two dimensions. A = whatever B = whatever...

22 days ago | 2

Answered
Using matrix to index another matrix?
Does this do what you want: x = sub2ind(size(B),(1:size(A,1))',A(:,1),A(:,2),A(:,3)); Output = B(x);

22 days ago | 0

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Answered
Equivalent of c++'s NULL or python' s None in MATLAB
This will probably depend on how these are used downstream in your code and whether you have arrays of them to deal with. If th...

27 days ago | 1

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X Y Z angles of a D20 (icosahedron) for gravity projection
If you have the 3D normal vectors, then all you need to do is take the dot product between them and the "flat" face normal vecto...

27 days ago | 1

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Answered
modify a row of an array within a function
This can sometimes be done inplace depending on how you write the function and how you call the function. One requirement is yo...

29 days ago | 0

Answered
Operator '-' is not supported for operands of type 'function_handle'.
You are using u as both an input argument and a global function handle function A3 = odeFun(t, u) <-- input argument global R...

29 days ago | 0

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Solve a system of 3 second order ODE
You will need to change your scalar equations to vector equations, and you will need to change your derivative function to a vec...

29 days ago | 0

Answered
Need to speed up the generation of random numbers.
You could over generate a large matrix and then pick off the number of elements you need later. E.g., C = rand([5 size(A)]); T...

30 days ago | 0

Answered
How do i create a large matrix with a formula?
N = 1000; a = 2 * pi * f * T * (0:N-1)'; x = [cos(a) -sin(a)];

30 days ago | 1

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Matrix multiplication to get covariance matrix
@Tintin Milou MATLAB variables do not have a "symmetric" attribute flag that I know of. Just because you create a variable that...

30 days ago | 0

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Why can't complex integer arithmetic be done?
I think the main reason for disallowing integer array arithmetic in MATLAB is because of the ambiguity caused by the max(min( ))...

1 month ago | 1

Answered
How can I split C/C++ Code in multiple files and still use MEX
Use the -c option to compile the B and C stuff to produce only object files without any linking: mex -c B.c C.c Then compile y...

1 month ago | 1

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Answered
Matrix multiplication. Trying to get scalar solution
Those should be matrix multiples, not element-wise multiplies. Remove the dots. E.g., top=nMode * M * u0; bot=nMode * M * nM...

1 month ago | 0

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Answered
Adapt RK4 ODE Solver from first order to 2nd order
Try this for starters yt = zeros(numel(y0),length(h:tfinal)); %Memory Allocation And then maybe this is what is intended for i...

1 month ago | 0

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Answered
Error using vertcat Dimensions of arrays being concatenated are not consistent.
You have a mismatch in the number of arguments. E.g., this [V,y] = ode45(@(~,y) fun(del_h1,del_cp1,cp1),Vspan,y0); should be ...

1 month ago | 0

Answered
Replacing matrix n column values
E.g., temp = A(:,70:80); temp(temp<0) = 0; A(:,70:80) = temp;

1 month ago | 1

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