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James Tursa


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3.281 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 to solve a second order differential equations with matrices by using "ODE45"?
1/m is a scalar/3x3 hence the error. Normally I would advise backslash here, but that brings up another issue. If M, C, and K ...

alrededor de 17 horas ago | 2

Answered
Image read in MATLAB and C
An int is likely 4 bytes on your machine, not 2 bytes. Also the expression "order" by itself evaluates as a pointer to the firs...

5 días ago | 0

Answered
Appending a row vector into a matrix based on given conditions
x = abs(b-60) > abs(b-550); % fixed typo xzplane550 = equakemat(x,:); xzplane60 = equakemat(~x,:); If all the data ends up in...

5 días ago | 0

| accepted

Answered
Is it a mistake that the function sum?
Welcome to the world of floating point arithmetic. https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1...

6 días ago | 1

Answered
return any angle to (0 to 2pi) range
The short answer: mod(x,2*pi) The long answer for this particular mod operation, is that if you want to get the same answer fo...

7 días ago | 0

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Answered
Precision quandaries: why can I print 64 digits?
What you describe sounds like it is just a display issue. Earlier versions of MATLAB on PC machines used a library print functi...

7 días ago | 0

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Answered
Grabbing number from array to calculate the numerical derivative
For the version you post, see the diff( ) function along with element-wise divide. E.g., diff(y) ./ diff(x) If that doesn't wo...

8 días ago | 0

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Answered
Coding a quadratic root finder
I would advise having your logic figure out what situation you have before you start solving things. E.g., something like if( a...

8 días ago | 0

Answered
Numerical solution of ODEs system using ODE45
You've got a 2nd order DE and a 3rd order DE, so the order of your system is 2+3=5, not 6. So your state vector should have 5 e...

8 días ago | 1

Answered
Am I doing this right? (a Math formula to Matlab language)
You are on the right track, but have typos in the code due to parentheses issues. A = sum( (x - y).^2 ); B = sum( (x - mean(x)...

9 días ago | 1

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Answered
Numerical solution of Higher order differential equation using ODE45 and a m. archice
t is a number, not a symbol. So u = sin(t) is a number, not a symbolic function. So doing diff(u) does diff on a single value,...

9 días ago | 0

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Answered
Write an executable script file (m-file) that takes no inputs and returns the displacement and stored energy of a spring system after prompting the user for the 1) input forces (in N) on the spring and 2) the spring constant (in N/m).
To get you started, simply create an m-file with something like this at the front end: F = input('Input the force on the spring...

11 días ago | 0

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Answered
How can I add 1 to a particular element in a matrix?
M = your 13x13 matrix M(1,2) = M(1,2) + 1;

12 días ago | 0

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Answered
How to determine Simplex using Nelder-Mead Algorithm in all direction?
The Nelder-Mead Simplex Method is an adaptive method that adjusts the lengths and directions dynamically. The vertices could be ...

13 días ago | 0

Answered
Question on why tilde cannot return the opposite statement result
Precedence of ~ is hgher than >, so it gets performed first. You need to use parentheses: ~(adultdata.age>50)

13 días ago | 0

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Answered
A single column vector or an array, which is faster?
Other things you are doing in your code are likely to dominate run times. We would need to see your particular application to of...

14 días ago | 0

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Answered
Matrices and indexing ?!
[LX,LY] = ndgrid(Lx,Ly); z = LX(:)./LY(:) <= 2; LX = LX(z); LY = LY(z); LX and LY contain the number pairs that match the co...

14 días ago | 0

Answered
Sort rows of matrix by matching column with another matrix column
E.g., assuming everything in column 31 has a match [~,x] = ismember(A(:,31),B(:,31)); Bsort = B(x,:);

14 días ago | 1

| accepted

Answered
how to find max value of a function with a for loop
Make e a vector. E.g., for i=1:length(x) e(i) = y(i) - (m*x(i)-b); % <-- Are you sure that isn't supposed to be (m*x(i) +...

14 días ago | 1

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Answered
How to solve a system of ODEs and plot the result
This is where you needed to show us the complete code and the complete error message. It is probably complaining about your init...

15 días ago | 0

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Answered
precision of calculation with Matlab
Calculators may not use the same floating point representations or arithmetic routines that MATLAB uses, so differences in the t...

15 días ago | 0

Answered
How to code for this equation in Matlab
Assuming that f(x) is really supposed to be f(t): f = @(t)exp(j*w*t); But, you will need to have w defined prior to this.

15 días ago | 0

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Answered
Mex C file generation Linker library error
Do you already have a zzz.lib file? Normally to get your mexFunction code to link to the library you simply include it as part ...

15 días ago | 0

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Answered
rand command give different answer
rand( ) is a random number generator ... it is supposed to give a different result. doc rand If you want to start over with th...

16 días ago | 1

Answered
Help creating an array to hold approx error from a taylor series
Generally, just index into your variable inside the loop: a_values(index) = a_err; If the indexing could be large, you would a...

18 días ago | 0

Answered
What is the Aerospace Blockset quaternion convention?
See also the Answer in this post: https://www.mathworks.com/matlabcentral/answers/465053-rotation-order-of-quatrotate

18 días ago | 0

Answered
angle between three points (in 3D)?
See the discussion in these links: https://www.mathworks.com/matlabcentral/answers/101590-how-can-i-determine-the-angle-between...

19 días ago | 0

Answered
How to convert char to uint8 and vice versa without changing the underlying data
Simply: c = original char array u = uint8(c); Or u = original uint8 array c = char(u); If you mean you want to reinterpret...

21 días ago | 0

Answered
Multiplying each column of a matrix with a specific value
mat=[2,1,0,0;1,0,0,0;0,0,0,1]; % 2D matrix f = [25,5,10,1]; % row vector result = f .* mat; % element-wise multiply with virtu...

21 días ago | 0

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