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James Tursa


Last seen: Today
3,819 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
How do i transform a second grade ODE into coordinates?
Looks like motion is restricted to be on the x-y plane, so r is 2D. You have a 2nd order ODE in a 2D frame, so that means you h...

17 hours ago | 0

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Answered
Runge-Kutta 4 implemetation blowing up
s(:,i+1) = s(:,i) + 1/6*(k1 + 2*k2 + 2*k3 + k4); % changed s(:,i+1) to s(:,i) on rhs

17 hours ago | 0

Answered
Need help with error checking
There are various ways to code this, but keeping the same basic architecture you have chosen you could do this: while( true ) ...

1 day ago | 0

Answered
Assignment has more non-singleton rhs dimensions than non-singleton subscripts ERROR IN FOR LOOP
x(:,i+1)=x(:,i)+A*x(:,i)+B*u(:,i); % changed u(i) to u(:,i)

3 days ago | 0

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Answered
Runge Kutta integration problem - NaN result
You may have a stiff DE and you can't use RK4 with a fixed step size. What happens when you call ode45( ) instead of ode15s( )?...

5 days ago | 0

Answered
Calculating the height of a liquid in a sphere using secant method
You need to use a function that is 0 at the h you are looking for. So you need that 30 in your function handle. E.g., func = @(...

6 days ago | 0

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Answered
Not enough input arguments
You need to call the function with the N input you just got from the user. E.g., disp(quiz6_func1(x,N))

6 days ago | 1

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Answered
ode45 function array error
You have tm(1) = 0, so using tm(1) as an index is invalid: tm=[0 30 etc... : for i=1:length(tm) : Ss_in(tm(i):end)...

6 days ago | 0

Answered
Is FORMAT DEBUG still any useful?
Strange behavior and probably deserves a bug report. E.g., R2019a: >> x = 1; >> y = x; >> x = x + 1; >> format debug >> y...

6 days ago | 0

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Answered
Precision (decimal digits) are very low and digits(32) does not help.
This is likely just a display issue and you don't need the Symbolic Toolbox. MATLAB does regular calculations in full double pr...

6 days ago | 0

Answered
Consecutive subtraction of the entries of a vector
If A is a row vector: B = [A(1) diff(A)]; If A is a column vector: B = [A(1);diff(A)];

7 days ago | 0

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Answered
generate random number with total sum is 10
Not sure from your wording if you want the row sums to be 1 or 10. If it is 1, then r = rand(6,1); r(:,2) = 1 - r(:,1); Modif...

7 days ago | 0

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Answered
when does changing variable's value affects its structure address?
In addition to what Walter has written, I would point out that all of the rules for variable creation, assignment, and sharing h...

7 days ago | 0

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Answered
Replace the numbers in an array
A(~isnan(A)) = B;

8 days ago | 1

Answered
Vector ODE using forward Euler method
Also your main code should look something like this: g = 9.8; mu = 0.5; [t,y]=ode45(@(t,y)rhs_1(t,y,g,mu),[0 100],[0.1; 0]); ...

9 days ago | 0

Answered
unique function return value of duplicate vector entry
Why can't you just use ind1 and ind2? E.g., V1_1 = V1_1(ind1); V2_1 = V2_1(ind1); V1_2 = V1_2(ind2); V2_2 = V2_2(ind2);

12 days ago | 0

Answered
Insignificant modification of code leads to NaN
Think about what is happening with this loop: for i = 1:num_iterates x = A*x; R(:,i) = x/norm(x); %%%% Problem Line %...

21 days ago | 1

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Answered
Skip instance of a loop with error
Something like this: try fn = x+y+z; %The function is just a representation. I am actually performing a Fi...

21 days ago | 0

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Answered
Performance of applications that are developed in MATLAB versus C++/C
Any such comparison will depend on exactly what computations are in question. A general comparison of languages probably isn't ...

22 days ago | 2

Answered
Numerical Integration by Matlab
Hint: You might look here: https://en.wikipedia.org/wiki/Normal_distribution Knowing that the integral of the Normal density f...

22 days ago | 0

Answered
Does MEX compiler (and the associated shared files) automatically ship with all MATLAB distributions of any license type?
Mex routines are not guaranteed to be compatible between different versions of MATLAB, for the very dependency reasons you alrea...

22 days ago | 1

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Answered
function call returns "index (1.2): subscripts must be either integers 1 to (2^63)-1"
You are missing a multiply operator. There is no implied multiplication in MATLAB with the 2( combination. E.g., u_1 = @(y) ...

24 days ago | 0

Answered
Mex, how to copy an array to output
See the solutions I posted here: https://www.mathworks.com/matlabcentral/answers/702682-with-mxmalloc-and-mxsetdoubles-mex-func...

24 days ago | 0

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Answered
With mxMalloc() and mxSetDoubles(), mex function crash matlab
You have memory leaks in your current code. E.g., tmpResult = mxMalloc(numRows*numRows*sizeof(*tmpResult)); // this memory ...

24 days ago | 2

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Answered
hi I am trying to use this code to solve RK4 equation and I keep receiving this error . what should I do?
Your implementation has several errors: Looks like you are creating i as a vector and then using that for indexing in A(i) You...

27 days ago | 0

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Answered
Filling in multidimensional array efficiently
Something like this maybe? k = 1; % your loop b = r x 1800 matrix f = whatever ch = whatever r = size(b,1)...

27 days ago | 0

Answered
extract out values out of loop
Make them arrays and assign to the elements. E.g., for i= 1: length(Hi) [XYZ(:,i),H(i),D(i),I(i),F(i)] = wrldmagm(Hi(i),La...

28 days ago | 1

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Answered
Projectile motion with drag. My problem is in the loop as the number of elements are not equal apparently on the left and right. Id appreciate detailed input ive been lost on this for a couple of days now
This makes AccDrag a vector: AccDrag(1,:) = [AccDragX(1) AccDragY(1) 0] So here you have a vector on the right hand side and a...

28 days ago | 0

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Answered
calling another matrix in a matrix
Don't do this! Creating numbered named variables in your code like yakit_1, yakit_2, etc. leads to downstream coding problems a...

28 days ago | 0

Answered
Newton Raphson Method in a for loop
You don't have the Newton-Raphson method coded correctly. You need to update the x value you use for the delta within the loop ...

28 days ago | 0

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