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James Tursa


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3.954 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
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...

3 días 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...

3 días ago | 0

Answered
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?

5 días 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...

6 días ago | 1

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Answered
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...

6 días ago | 0

Answered
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. ...

6 días ago | 0

Answered
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...

6 días 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...

7 días 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; ...

7 días 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...

7 días 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...

7 días ago | 0

Answered
Calculating a matrix with a specific form
You could rearrange the equations, isolate m(1), m(2), and m(3) and solve for them directly. E.g., rearrange the equations to f...

8 días ago | 2

Answered
Combine logical arrays into one array
L = L1 | L2 | L3 | L4;

8 días ago | 0

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Answered
How to vectorise code involving matrix multiplications with vectors
See this link: https://www.mathworks.com/matlabcentral/answers/776812-how-to-vectorize-a-b-operation-on-slices-of-3d-matrices?s...

8 días ago | 0

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Answered
What is the corect code for writing an error message when a user inputs an array instead of a scalar value?
Several ways to test for a scalar. E.g., if( ~isscalar(x) ) error('Input is not a scalar'); end or if( numel(x) ~= 1 )...

8 días ago | 0

Answered
Calculating and and recording a vector during each iteration of a "while" loop.
E.g., using a counter to store all of your iteration data in a cell array and then post process this: k = 1; % the counter Rce...

8 días ago | 0

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Answered
Trying to separate Quaternion coefficients into array.
Use the double( ) function to convert to numeric array, then use regular indexing. E.g., try this function g = actfun(q) ...

8 días ago | 1

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Answered
quat2eul is giving me a strange result
Maybe all you have to do is add 2*pi to all results that are less than -pi to get things how you want.

13 días ago | 0

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Answered
Handling Inputs mex function
The prhs[ ] variables are of type pointer to mxArray ... you cannot use simple native C conversions with them. You must use som...

15 días ago | 0

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Answered
How can I fix this error?
Delete the extra closing parentheses. I.e., delete the paren where the red underline is.

16 días ago | 0

Answered
Undefined function or variable t
Put this code in a separate file called Math.m % file Math.m function dxdt=Math(t,x1) % function name x=x1(1) y=x1(2) z=x1(...

16 días ago | 0

Answered
Generating a 4th order Runge-Kutta Integrator solver for the motion equation.
ode45( ) is not well suited to the orbit problem since the integration errors can systematically build up over time. You can tr...

16 días ago | 0

Answered
ODE45 function for 3 Variables
This y0 = [0;0;0;0]; and this zF = 0; means that your derivative function will evaluate to 0 exactly, so the solution is 0 e...

16 días ago | 0

Answered
Can anyone help?
Hint: Look at the results of this operation, and I think you can figure it out from there: x = [2;3;4]; % column vector y = 0:...

29 días ago | 0

Answered
How binary Random number generation upto n nodes ?
Here is how to get your stated desired output, but this is not random at all: r = dec2bin(0:(2^L-1)) - '0';

alrededor de 1 mes ago | 0

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Answered
Undefined function or variable 'bisection'.
From the error message, it looks like you are calling the function using the name "bisection", but the actual name of the functi...

alrededor de 1 mes ago | 0

Answered
ODE45 in 3 dimensions with 6 initial conditions
I find it easier to keep the position elements together, and the velocity elements together, in the state vector. So I would de...

alrededor de 1 mes ago | 1

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Answered
Generate a Runge-Kutta Integrator solver for the orbital motion equation, when given the initial conditions. Execute for 500 seconds.
First, I find it easier to keep the position elements together, and the velocity elements together, in the state vector. So I w...

alrededor de 1 mes ago | 1

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Answered
Runge-Kutta method, cannot produce the correct graphs
You need to index x in your calculations. E.g., q1 = f(x(i),y(i)); q2 = f(x(i)+h, y(i)+h*q1); You should init...

alrededor de 1 mes ago | 0

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Answered
Working with an equation and variables from user.
You can construct a function handle as follows: f = str2func(['@(x,y)' str1]); You can then use this function handle to evalua...

alrededor de 1 mes ago | 0

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