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# James Tursa

Last seen: 27 dagar ago 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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How to call function repeatedly using arrays as variables?
There are other ways do to this, but to answer your question about how to turn the code into a loop, use indexing based on the n...

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Best Practice: Many Functions relying on Global Variables?
See this link for a related discussion involving the best way to define global constants, in particular Steven Lord's answer: h...

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Use Matlab to find the acceleration and jerk of the body with velocity
Take the derivative of velocity to get acceleration. Take the derivative of acceleration to get jerk. Since you have an explic...

floating-point arithmetic
"... the IEEE754 conversion of 0.1234 and 0.123 have infinite digits ..." Not sure what you mean by this statement. Neither of ...

random number generating RANDI with percentage
One way: n = 1000; p = 0.86; r = rand(n,1); x = r < p; m = sum(x); r(x) = randi([0,14],m,1); r(~x) = randi([15,28],n-m,1)...

Points inside the sphere
Just plug your points into the ellipsoid equation and see if they work. E.g., ((x - X)/a).^2 + ((y - Y)/b).^2 + ((z - Z)/c).^2 ...

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Strange output from symbolic calculation
This isn't strange at all. You are asking the Symbolic Engine to examine all floating point expressions involving pi, which isn'...

I keep getting an error?
Generally, these types of problems are solved by extracting the contents of the cell instead of using the cell itself. E.g., C ...

3D sparse matrices
You can use the ndSparse FEX submission by Matt J: https://www.mathworks.com/matlabcentral/fileexchange/29832-n-dimensional-spa...

Convert Fortran to MATLAB
Here is the equivalent MATLAB code: NB = 100; F = 0; for i=1:NB % [some equations] if( abs(xm) < wm ) ym ...

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What is the difference between a^3 and a.^3 if a is a matrix?
E = C^3 is a matrix power, equivalent to E = C*C*C, where these are all matrix multiplies. D = C.^3 is element-wise power, wher...

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Need Help for the rest of this coding
This is very basic vector construction and indexing. I suggest you take the MATLAB Onramp tutorials found here: https://www.mat...

Malfunction to my matrix calculation
K .* F (with the dot) does element-wise multiplication with implicit array expansion if the variables are different sizes, thus ...

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How do I write this c++ for loop statement in Matlab for loop?
E.g., using a while loop (changed max and min to maxx and minn): x = j; while( maxx >= minn && x <= m+r ) % body of loop ...

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why my matlab code calculates the inequality wrongly?
Negative numbers are not greater than positive numbers. This is the correct result. What is strange to you about this?

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RK4 Method for Windkessel error
Multiple errors. When you call your function handle f, it is assumed that the P and Q are values passed at time t. They are not ...

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Use a for loop to determine the sum of the first ten even terms in the series 5k3 (k=2, 4, 6, ….)
You are summing all the terms with 2:10. For the "even" terms you need to skip the odd ones, so the range would be 2:2:something...

Polt an object in uniform circular motion with Euler method
So you have made a good start, but you have errors in your derivatives ... why do you have t's in your derivative equations? The...

How to solve a non-linear system of differential equations?
Your equations are linear in the derivatives, so you can form your equations as a matrix equation, then write a derivative funct...

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What do I need to change to get my Improved Euler's to match my Euler's?
Your current code is hard to read and debug because you have multiple variations of this expression scattered throughout your co...

How do i use fminsearch to find the minimum or maximum of a function . x.^4-3.*x.*y+2.*y.^2
You need to have your function handle accept a vector and return a scalar. I.e., the x argument to the function handle is a vect...

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Optimization of Rocket Launch
You have proposed work that IMO is way beyond what is achievable with your code. Constrained optimization of this sort is not tr...

how to split a string (char value) with zero in front of it but showing the value in the matrix?
Two more ways: S = '0100'; S=='0' % logical result S-'0' % double result

Manual MEX vs MEX by codegen
MATLAB does not publish the "rules" that Codegen uses to generate mex code. Because it is automated, I am not surprised that the...

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Solve 2nd order ODE using Euler Method
You start your loop with i=1, but that means your x_d(i-1) will be x_d(0), an invalid index, hence the error. You need to set in...

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Finding a single root of x^(3.6)=75
Make a function handle with the @ operator. E.g., fun = @(x) x^(3.6)-75; x0=3; z = fzero(fun,x0) Check z^3.6 Or you can r...

Need to find dot product between two second order tensor
If you change the inner loop calculation to this: w(i,k) = dot(S(i,:),u(:,k)); then you would have dot products between the S ...

linear combination of vector and permutation
Another way very similar to Torsten's method, limited to two desired values: n = 3; 2*(dec2bin(0:2^n-1)-'0')-1