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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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Increased time for setting elements in sparse matrix
Every time you change the elements of a sparse matrix, MATLAB has to deep copy all the existing elements to a newly allocated ch...

ongeveer 7 uur ago | 1

How to run a Matlab file which uses functions from .c and .dll files?
It appears that this may be an older mex routine? Is there a "mexFunction" in the c file? If so, maybe you can just recompile it...

6 dagen ago | 1

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Unable to perform assignment because the left and right sides have a different number of elements.
Why are you replacing the sin(y-c) term with approximations? Why haven't you just programmed it as is? It appears you have done ...

9 dagen ago | 0

Applying runge kutta for coupled equations
What are and ? Why don't they have differential equations associated with them? Can you give more details about this? Also, it...

9 dagen ago | 0

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How to create a loop on function handle
Isn't this just a standard matrix*vector multiply? E.g., XI = @(xi) xi - (y(i,:) + A*((t(i)+c*dt).*xi)*dt); Note that this fun...

12 dagen ago | 1

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Index Matrix A and Matrix B Problems
You can use logical indexing: B(A==1) = 0; You can use a loop for this also, but you would have to show us the code you used b...

12 dagen ago | 1

Whole derivation of two variable differential function
Please show the code you are using. y' means derivative of y with respect to x, not derivative of y with respect to y. You sho...

13 dagen ago | 0

How do i compile multiple fortran code from matlab command
To pass variables from MATLAB to your Fortran code you would typically do the following: Write a single gateway routine in a se...

26 dagen ago | 0

Updating Sparse Matrices every Time-Step Efficiently
To specify the sparse matrix size when creating it, use the following syntax: sparse(I,J,K,m,n) where m is the number of rows ...

26 dagen ago | 0

how to move a row
result = M([1:400,801,401:800,802])

26 dagen ago | 1

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How to set specific size of a figure with exportgraphics?
This doesn't answer your question about controlling exported sizes, but you might be interested in the following export_fig FEX ...

27 dagen ago | 0

Renaming the variabel while Symbolic to function handle conversion with matlabFunction
You could keep your existing code and create another function handle: funcv = @(A,xdata,ydata)func(A(1),A(2),xdata,ydata)

28 dagen ago | 0

Making an Array out of another Array if conditions are met
You don't need a for-loop for this. The best way is to use logical indexing. See this link: https://www.mathworks.com/help/matl...

29 dagen ago | 0

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How to remove February 29th for leap years in a daily time series over 43 years?
To get rid of the leap days, you can use evenly spaced indexing since the number of days between leap days is constant for your ...

ongeveer een maand ago | 0

I would like to write a for loop to store all values of y when A=1,2,3,4,5. into a variable y1,y2,y3,y4,y5 respectively. Any help will be greatly appreciated. Thanks
No loop needed, and no need to create multiple variables to hold results. Just use implicit array expansion and hold results in ...

ongeveer een maand ago | 0

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Index in position 1 is invalid. Array indices must be positive integers or logical values.
Looks like you changed the definition of what f_m is in your code. In these lines f_m appears to be an array intended to hold va...

ongeveer een maand ago | 1

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...

ongeveer 2 maanden ago | 1

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 ...

ongeveer 2 maanden ago | 0

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

ongeveer 2 maanden ago | 1

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...

ongeveer 2 maanden ago | 0

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...

ongeveer 2 maanden ago | 0

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...

ongeveer 2 maanden ago | 0

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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 ...

ongeveer 2 maanden ago | 0

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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,-...

2 maanden ago | 0

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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...

2 maanden ago | 0

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...

2 maanden ago | 0

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 ...

3 maanden ago | 0

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_...

3 maanden ago | 0