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James Tursa


Last seen: Today 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
Change of position of velocity vectors and time interval between the change
Looks like an orbit problem. Around the Earth, I presume? You will not be using the Symbolic Toolbox for this assignment. You w...

2 days ago | 1

Answered
Any comment to speed up the speed of caculation of symbolic loops having Legendre polynomials?
The Symbolic Toolbox is going to be slower than IEEE floating point ... that's just something you have to accept. And if you nee...

6 days ago | 1

Answered
Formula for norm(x)
This question appears to be a follow-up to this post: https://www.mathworks.com/matlabcentral/answers/1809695-what-exactly-norm...

6 days ago | 0

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Answered
what exactly norm(x) function do?
The equivalent function to norm( ) for a complex column vector x is sqrt(x' * x) where x' is the complex conjugate transpose. ...

7 days ago | 1

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Answered
Why am I receiving Not enough input arguments?
The error seems pretty clear, you are calling func( ) without enough input arguments. The func( ) signature has six inputs: fun...

7 days ago | 1

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Answered
I have some coupled nonlinear ordinary differential equations. Three equations have three 2nd order derivative coupled together. Can someone tell me how I can get the response
Another related approach is to isolate all the 2nd derivatives on the LHS and put everything else on the RHS. Then pick off the ...

8 days ago | 0

Answered
how to use exp for this problem
You need to use the * operator to multiply in the denominator. E.g., w=exp(-(i-Un)^2/(2*sd^2)) If i is not a variable defined ...

8 days ago | 0

Answered
Multiple Outputs of a function into a single vector
You could modify f( ) to return a vector. Or if you didn't want to modify f( ) you could create a helper function that does this...

8 days ago | 1

Answered
dynamic matrix with changing variable name in for loop
Do not dynamically name variables. This is bad programming practice and will leave you with hard-to-use variables downstream in ...

8 days ago | 0

Answered
ODE solver for restricted 3 body problem
In this line: dydt(2) = y(1) + 2 * dydt(3) - mu_p * ((y(1) + mu)/D1) - mu * ((y(1) - mu)/D2); you use dydt(3) before you set i...

9 days ago | 0

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Answered
Write a function file that computes the roots of a quadratic using the form for x+ and x−1 that are least susceptible to cancellation error.
Is this the type of formulae you are being asked to code? https://people.csail.mit.edu/bkph/articles/Quadratics.pdf https://st...

10 days ago | 0

Answered
How to get the same number of char as number of decimals using num2str?
You might look into using the fix( ) function to isolate the fractional part of your number and then work with that directly.

13 days ago | 0

Answered
matrix to struct do not match
You should really show us all of the actual code in question, not just a wordy description of the code. A better description and...

14 days ago | 0

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Answered
Assign elements in multidimensional struct to 2D array
You can use the vercat( ) function to force the comma-separated-list generated by C.pts to stack vertically: for ii=1:5, C(ii)....

15 days ago | 1

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Answered
Singular Value Decomposition calculation of a matrix
By changing the order of the rows you have changed the order of operations inside svd( ). The two answers are essentially the sa...

16 days ago | 1

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Answered
Issue with N body problem using ode45
You need to rethink your problem statement and initial conditions. The initial positions can't possibly be in the neighborhood o...

22 days ago | 0

Answered
What is the best function of the following shape?
There are lots of functions that could fit this general shape. E.g., sin(x), or more generally A*sin(B*x+C) depending on width a...

22 days ago | 0

Answered
Rotate an image 180 degrees without library functions
Hint: Take a small example, rotate it 180 degrees, and see where the elements end up. Then consider how you might get that resul...

24 days ago | 0

Answered
How to rearrange columns in a MATRIX?
One way: [X(:,1:2);X(:,3:4)]

25 days ago | 0

Answered
How to calculate the mean value of the non vero value in a vector?
Another way that doesn't require any data copying: M = [0.7,0.3,0]; sum(M)/nnz(M) Be aware that if there are no non-zero elem...

26 days ago | 1

Answered
Adding value from structure into a vector after each iteration of a for loop.
The reason you are getting a 2x8x2 answer is because you start with a 1x8 vector but then assign spots outside of those limits i...

29 days ago | 0

Answered
parallel sum different from serial sum
Bruno and IA have already given the reasons for this discrepancy. I would simply add that even though you are adding integers an...

1 month ago | 2

Answered
how to multiply quaternion wth 1x3 vector
Use BECI as the "vector" part of a quaternion and put a 0 in the "scalar" part, and use that new quaternion in the multiply. Sin...

1 month ago | 1

Answered
I want to convert vector into matrix with all possible combinations
I think John D'Errico answered this some time ago, or a question very much like this. But I can't find his post at the moment. I...

1 month ago | 0

Answered
Can compare between vector and array
Does this do what you want? Finds the row numbers in A that match x. find(all(A==x,2))

1 month ago | 0

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Answered
Modify off diagonal elements of Matrix without looping
You could use logical indexing to get at the off-diagonal elements. E.g., A(~eye(size(A))) = skalar;

1 month ago | 0

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Answered
How to get two 16-bit numbers from a 32bit number
E.g., to split a uint32 into two uint16 you can use typecast( ): result = typecast(your_variable,'uint16') This result will co...

1 month ago | 0

Answered
pass a vector from matlab to a c++ program
This really depends on what your C++ program does, but the simplest approach is to use a mex routine. You will need a supported ...

2 months ago | 0

Answered
Write multiple variables from a function
Maybe something like this does what you want, with each qq1 and qq2 2D page results in the first two dimensions. [m n] = size(s...

2 months ago | 0

Answered
In an assignment A(I) = B, the number of elements in B and I must be the same.
" And in the work space y2 is 3x1 and d is 1x1 " Then d - y2 will be 3x1. You can't assign a 3-element vector to a 1x1 scalar w...

2 months ago | 0

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