James Tursa

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3,973 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
Replacing matrix n column values
E.g., temp = A(:,70:80); temp(temp<0) = 0; A(:,70:80) = temp;

4 hours ago | 0

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Solving an overdetermined system of linear equations
Since you can simply plug in those values to verify that they satisfy all four equations, the conclusion would be that you have ...

5 hours ago | 0

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How to create a cell array with binary numbers?
Your pop variable has 1000x11 = 11000 elements. Your for-loop only assigns values to 1000 of those elements (the first column)....

5 hours ago | 0

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Vector sum of forces
sqrt(sum(F.*F,2))

19 hours ago | 0

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invalid use of operator
You are missing a ( after the second "if", and you are missing an "end" statement. That being said, my suggestion would be to u...

3 days ago | 0

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Need Help Solving Two Coupled ODEs
The derivative function needs to have the input arguments specified. In your current code above, you have no inputs specified. ...

7 days ago | 0

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Answered
Versions of Euler Methods
methodA has a fundamental flaw: y(i+1) = y(i)+ h*func( t(i) + h/2, (y(i)+y(i+1))/2 ); You can't use y(i+1) on the right hand s...

7 days ago | 1

Answered
Problem with matrix differential equation resolve in Matlab with ode45
Normally I would have expected ode45( ) to pass q as a 4x1 column vector. Also, I don't see anything in your code solving for q...

10 days ago | 0

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Answered
Question regarding quaternion conventions; particularly with respect to point vs frame rotations
See this post for comments regarding "point" vs "frame" convention: https://www.mathworks.com/matlabcentral/answers/524471-what...

10 days ago | 0

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Using vectorization to shorten run time
E.g., [P,D] = meshgrid(p,d); % generate all possible combinations X = [P(:) D(:)]; % combine them into side-by-side column vec...

14 days ago | 1

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Answered
why does dimension of input variable change in ode45
The dimension changes to a column vector because that is the way ode45( ) operates. Your derivative function needs to be able t...

14 days ago | 1

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Answered
Maatlab crash with .mex function
I had to make some assumptions about how the matrix data areas are supposed to be loaded. We can try this first to see if these...

14 days ago | 0

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How to calculate standard deviation in double for loop?
The short answer is don't do that. This style of programming has many problems. See this link for alternatives: https://www.m...

15 days ago | 0

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Add row to an empty array if a condition is fulfilled
No need for an explicit loop. Just use logical indexing: result = m(strcmp(m(:,3),'A'),:);

15 days ago | 0

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Answered
reproduce random numbers for the third dimension
If you don't want the random numbers to change from iteration to iteration, then don't regenerate them inside the loop. Calcula...

15 days ago | 0

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Using an Array as an input
The error message actually tells you exactly what to do. Use element-wise operator .^ instead of the matrix operator ^ Energy ...

15 days ago | 1

Answered
Runge-Kutta 2
The + 4.*x1 should be - 4.*x1 in your derivative function. Also, using both X1 and x1 and X2 and x2, even though MATLAB is case...

15 days ago | 0

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Answered
3D array of rotation matrices multiplied on 2D array of vectors
To answer your side question of how to transpose 2D pages of an array, you can use the permute function to swap the first two di...

15 days ago | 0

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Passing structs/objects to functions
MATLAB typically passes shared data copies of input arguments to functions. That means creating a separate mxArray header for t...

17 days ago | 0

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How can I solve a system of ODE's, in which the equations have a dependency on time, as well as the other ODEs?
Just code it up as it appears using a 3-element state vector, where the elements are defined as follows y(1) = x y(2) = y y(3...

24 days ago | 0

Answered
How to improve the speed of large matrix addition?
If you are generating a new matrix C each time, then you are essentially doing two things: (1) Copying all the elements of A in...

24 days ago | 0

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Dealing with very small or very large numbers
I guess the obvious suggestion is to work in units of nanometers or maybe picometers instead of meters. Can you do that?

26 days ago | 0

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Answered
How to use if statement in function?
Add this code to the top of your function: if( N <= 0 ) error('N needs to be > 0') end That being said, your loop probab...

27 days ago | 1

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How to build a quaternion from a normal vector?
If you have the Aerospace Toolbox, you could do the following n = 1x3 unit normal vector a = angle to rotate in radians v = 1...

27 days ago | 0

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Runge-Kutta 2
Normally one would plot the position, not the velocity. So I would have expected you to plot the "1" index of your solutions. ...

27 days ago | 0

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Double Variable Second order Differential Equation
Just write a derivative function using four states instead of two. The states will be x, y, dxdt, and dydt. The derivitives of...

27 days ago | 1

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Answered
How can I divide each element of a vector by each of the elements of another vector in MATLAB?
Assuming a and b are both column vectors, you can use automatic array expansion by transposing one of them and using element-wis...

28 days ago | 0

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Answered
"Array indicies must be positive integers" error
You can't have 0 or fractional indexing in MATLAB. Take this section of code for example: for t = 0:1:200 U(0,t) = ui; ...

28 days ago | 0

Answered
what is the difference between the 2 codes ?
zeros([2,2]) passes one argument, a 2-element vector [2,2]. zeros(2,2) passes two arguments, the scalars 2 and 2. The result i...

28 days ago | 0

Answered
Getting all Permutations of a 18+ integer vector
The number of different permutations of a vector of size n is n! (n factorial). So what you are attempting has these many possi...

29 days ago | 0