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James Tursa


3.168 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
Rolling all six numbers on a six sided die
This: v = zeros(1,NToys); NRolls = 0; needs to be inside your Trial loop so that it resets for each trial. A simpler way to ...

alrededor de 2 horas ago | 0

Answered
Need help Euler Method
The fundamental thing you are doing wrong is that you don't have the proper size state vector. For a 1st order equation, the st...

alrededor de 3 horas ago | 0

Answered
How can I add values of an array as an input into the ode45 function ?
What is the size of I? What is the DE you are solving? Maybe just dropping the (t) will work: dydt= (-I/(3600*Q)); Or maybe ...

alrededor de 4 horas ago | 0

Answered
double differentiation and double integration of sine wave
"... when differentiating my position to get velocity and acclereation i did work out all three of them by hand, quite sure it i...

alrededor de 10 horas ago | 0

Answered
Comparison of two Vektors with different size to find variables
E.g., x = ismember(b(:,1:2),a(:,1:2),'rows'); c = b(x,:); Depending on how the times were constructed, you might need to use ...

alrededor de 10 horas ago | 0

Answered
How to transfer parameter between C and fortran
Maybe the Fortran compiler settings are compiling the default integer as 8-byte integers. Try forcing the Fortran to use 4-byte ...

alrededor de 19 horas ago | 0

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Answered
How to sort a matrix in a random order
E.g., >> x = reshape(1:24,4,6) x = 1 5 9 13 17 21 2 6 10 14 18 22 3 7 ...

1 día ago | 0

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Answered
can someone help me to solve this error (This statement is not inside any function. (It follows the END that terminates the definition of the function "RK4".)
Looks like your plot( etc ) and legend( etc ) lines are stuck inbetween two functions. Did you intend them to be inside a scrip...

2 días ago | 0

Answered
making array in for loop
Maybe prior to the loop define Alignment as a cell array to hold your results: Alignment = cell(10000,1);

5 días ago | 0

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Answered
Why is my function generating a vector? Please help?
A uniform random number between a and b is: u = a + rand*(b-a) Generate two of these with a = -0.05 and b = 0.05 and then do t...

7 días ago | 0

Answered
Can someone explain the concept of B= null(A) in simple words?
The columns of B form basis vectors for the "null space" of A. Any linear combination of the B columns, when multiplied by A, w...

7 días ago | 1

Answered
Unable to perform assignment because the size of the left side is 1-by-1 and the size of the right side is 5-by-1.
Looks like Cd and rho are vectors. So the result of those calculations on the right hand side will be vectors. But you are tryin...

7 días ago | 0

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Answered
What can I use instead of VPA?
See the following FEX submissions by John D'Errico: https://www.mathworks.com/matlabcentral/fileexchange/36534-hpf-a-big-decima...

8 días ago | 1

Answered
Two equal datetime values showing as unequal when compared?
This is often just a display issue. E.g., >> s = datetime(2017,3,24,9,5,0.1) s = 24-Mar-2017 09:05:00 >> t = datetime(20...

8 días ago | 0

Answered
How can I multiply square submatrices more efficiently?
Here is the naive mex code. Could probably be made faster by doing the for-loop in parallel or trying to optimize cache hits, b...

8 días ago | 1

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Answered
big difference in execution time in approximately the same code
The matrix multiply operator * in MATLAB calls highly optimized compiled BLAS library code in the background. The BLAS library ...

8 días ago | 2

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Answered
This is a question from numerical methods asking to explain what the code does for 12 marks.
https://en.wikipedia.org/wiki/Newton%27s_method

9 días ago | 0

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Answered
how to use passing by value and passing by reference
In the background, MATLAB effectively passes all variables into functions as shared data copies. This has the same effect as pas...

14 días ago | 0

Answered
matrix dimensions must agree error
Well, tau is only two elements and w is a lot more than that, so you can't multiply them element-wise like you are attempting to...

14 días ago | 0

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Answered
Monte Carlo integration of sin(x)
This is what you are currently doing with the "random counting in an area" method: To make it go from -1 to +1 instead, you c...

14 días ago | 0

Answered
How can i split the values of vector into group of 5?
Assuming your vector is divisible by 5, you could do this: v = your vector g = reshape(v,5,[]); % reshape v into a 5 x N matri...

15 días ago | 0

Answered
Runge-Kutta function with a second order ODE
I'm still confused about your initial conditions and what y0 and y1 are. But let's back up a bit. For a 2nd order ODE, your st...

15 días ago | 0

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Answered
how to call struct array in subroutine
See this related thread: https://www.mathworks.com/matlabcentral/answers/480829-what-is-the-best-way-to-insure-that-all-of-my-f...

15 días ago | 0

Answered
For and if loops
RT([3,6],v) is the syntax to use for the 3rd and 6th rows of the v'th column of RT. But this is of course going to be two eleme...

16 días ago | 0

Answered
Matlab Solving Differential Equation using Runge Kutta
In this line: k_1 = F_xy(x(i), xy(i)); You've got xy(i) as an argument, but there is no xy variable. I think you meant y(i) h...

19 días ago | 0

Answered
How can i write MacLaurin Sequence for 1/1+x2
An outline of your code could look something like this: x = _____; % you fill in the blank here, or get an input from the user ...

19 días ago | 0

Answered
Multiplication of complex matrices
There are two different operators: ' is the complex conjugate transpose .' is the straight transpose (no complex conjugate), n...

20 días ago | 1

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Answered
why MATLAB 2019b MEX file is slower
Impossible to say for sure without knowing what your mex function is doing. One thing to note is that in R2018a the storage for...

20 días ago | 3

Answered
Different complex log values displayed for a "single" input
This is simply the result of floating point calculation artifacts ... not a bug. For instance, your assertion that all of your ...

20 días ago | 0

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Answered
using ode45 for coupled equations
You are mixing syntax here: @(t,x)myfun Either use the syntax @(t,x)expression, where expression is the derivative or use the...

20 días ago | 0

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