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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
What does A(2:4) = [ ] do if A is a 3x3 matrix?
This is linear indexing. Even though the variable is a 2D matrix, MATLAB allows you to index into it using only one index. The l...

4 days ago | 1

Answered
error using function code
Create a file called lettergrade.m somewhere on the MATLAB path (e.g., in your working directory) edit lettergrade.m Copy all ...

4 days ago | 0

Answered
dynamic naming of structures
Would it be acceptable to use x as a dynamic fieldname instead of the top level variable name? E.g., v.(x).a v.(x).b

4 days ago | 1

Answered
How can I define an array of sparse matrix? (both for GPU and CPU)
For CPU, you can use the ndSparse submission by Matt J on the FEX: https://www.mathworks.com/matlabcentral/fileexchange/29832-n...

4 days ago | 0

Answered
numerical integration with recursive trapezoid rule
Some issues are immediately apparent. First, you don't reset S=0 inside the while loop. Isn't S supposed to contain only the a...

4 days ago | 0

Answered
Store every N columns in a Matrix to a new Matrix
Don't create a bunch of new matrices with hard to use names downstream in your code. Instead, simply reshape your matrix and the...

9 days ago | 0

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Answered
MEX file always crashes when I run it
In the MATLAB code you have this: np=single(np); Then inside the Fortran gateway routine you have this: mwPointer xr, yr, n ...

9 days ago | 0

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Answered
How can I reshape a matrix this way
a=[-0.26,0.23,0.033,0.1,-0.39,0.30;0.30,-0.39,0.10,-0.26,0.03,0.23;-0.03,-0.13,0.16,0.33,-0.16,-0.16] b=[-0.26,0.23,0.033;0.1,-...

15 days ago | 0

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Answered
Matlab while loops with equations
You should probably go through the online tutorials for learning MATLAB. But I will give you an outline to get started: toleran...

16 days ago | 0

Answered
i need to find error in code because I it's increasing but it should be decresing
You need to use all the derivatives at the first point to propagate for the initial guess at the second point. I.e., these lines...

17 days ago | 0

Answered
t = 2 s, i = √−1, and 𝜔=120π rad/s. Evaluate the following using MATLAB? Hint: exp(n) is used in MATLAB to evaluate en. (a) e−2𝑡𝑐o𝑠 (𝜔𝑡)
I am guessing that the original expression shown is supposed to be interpreted as: Then take the hint at how to evaluate the ...

1 month ago | 0

Answered
Why is my projectile motion code only working at certain input angles.
Drag depends on current velocity, not initial velocity. So you need to recalculate V at each step. E.g., Vx = Vx_new; Vy = Vy_...

1 month ago | 0

Answered
Sine equation in Euler Method ODE
You've only got one scalar differential equation, so I don't understand why you think you need two variables x and y along with ...

2 months ago | 0

Answered
subtract matrix from vector
Just learn how to use indexing and element-wise operators. From your language, here are the pieces: subtract - the first thre...

2 months ago | 0

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Answered
How can I create arrays with different names using loop?
Don't embed numbering into the variable names. This will make the variables hard to use downstream in your code. Use cell arrays...

2 months ago | 0

Answered
How to subtract each column of a matrix from a column vector?
Just do a usual subtraction and let MATLAB implicit expansion kick in: M = your matrix v = your column vector result = v - M;...

2 months ago | 0

Answered
Simple mex file crash?
You need to create the output variable yourself. plhs[0] doesn't exist until you create it, thus this line crashes: outData = m...

2 months ago | 0

Answered
Simulating Projectile with Matlab
You don't show us both methods (with and without drag) so we can't compare them. I presume you simply set k=0 for the case witho...

2 months ago | 1

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Answered
Matlab simulation for planet motion
The initial condition for position and velocity need to be outside the loop, prior to loop entry.

2 months ago | 1

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Answered
Vector ODE solution is not periodic/ as expected
This index 4 dxdt(4) = -DU^2* x(3)/sqrt(x(1)^2+x(2)^2+x(3)^2)^3; needs to be index 6: dxdt(6) = -DU^2* x(3)/sqrt(x(1)^2+x(2)^...

2 months ago | 0

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Answered
How to compile a Fortran subroutine by using the MEX engine
It looks like you are taking input, calling a MATLAB function, and getting output from that function. I still say it would be ea...

2 months ago | 0

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Answered
How to create Matrix [1 2 3 4; 2 4 6 8; 3 6 9 12; 4 8 12 16] without using loops or any functions using loops?
n = 4; % whatever result = (1:n) .* (1:n)' % use implicit expansion row .* column

2 months ago | 2

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Answered
Vectorising Multiplying each column from a matrix with a square matrix and the tranpose of this column
If you need the same column on each side of the multiply, then maybe this: result = sum(h'*Pn.*h',2);

3 months ago | 1

Answered
Problem in using mxSetPr with USHORT
To attach pointers of type other than double to an mxArray, you can use the mxSetData( ) function as Jan suggests. In your case ...

3 months ago | 1

Answered
Beginner coding; my second, simpler approach at trying to make all elements distinct.
FYI, to generate random integers you can use the randi( ) function instead of ceil(value*rand( )): https://www.mathworks.com/he...

3 months ago | 0

Answered
How to make a "page transpose" in a 3D matrix without using the function pagetranspose?
Mtranspose = permute(M,[2 1 3]);

3 months ago | 2

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Answered
How to multiply an inverse matrix (nxn) by an array (nx1) using for loop
Not sure why you have a for-loop at all. Maybe you can explain this. If you just want to multiply the explicit inverse by a vect...

3 months ago | 0

Answered
Adding numbers to an array
You don't really need both h and hnew. Just use h and some indexing. E.g., h = zeros(1,45); % allocate expected result k = 1; ...

4 months ago | 0

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Answered
rounding issues in matlab, need to force values to 0
Instead of if abs(y1)< 1e-6 y1=0; end try y1(abs(y1)<1e-6) = 0;

4 months ago | 2

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Answered
why will the area only work for the circle and not the other shapes
To compare strings, do not use the == operator which does an elementwise compare. Instead, use a function meant for comparing st...

4 months ago | 0

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