Community Profile # James Tursa

Last seen: 1 day 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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Mean computaion in matlab
You can specify the dimension to use with the mean( ) function. E.g., maybe this is the computation you want: data = your 3D m...

2 days ago | 0

What is the mean?
B' is the complex conjugate transpose of B. If B is real, then it is equivalent to just the tranpose and the assignment simply ...

3 days ago | 0

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How can I model equation of motion (2nd order ODE) when system matrices are in terms of state variables?
Yes you can have derivative functions that depend on state variables. This is quite common. E.g., define a 4x1 state vector y th...

5 days ago | 0

empty double matrix in case of nul value
Do you mean you want to do something like this: if( isempty(malicious) ) malicious = 0; end

14 days ago | 0

To allocate character array='2a'
'2a' is a two element character string. You can't assign two elements to a single element. I.e., you can't assign a 1x2 vector...

17 days ago | 0

How to get the desired quaternion representation from a rotation matrix?
As you already know, both q and -q represent the same rotation. Which sign to pick is entirely up to the underlying algorithm. ...

26 days ago | 0

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Implementation of Runge Kutta Numerical Solution for system of ODE's
The main technical problem (other than your syntax not being MATLAB) is that you are trying to solve your four 1st order equatio...

1 month ago | 0

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How to convert complex float to complex integer in MEX gateway function?
I would guess you can just use the appropriate data types. E.g., mxComplexInt32* Data1 = mxGetComplexInt32s(prhs); mxComp...

1 month ago | 0

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Can you help me with this loop?
Can you use num2str? Message = [num2str(TotalMinutes) ' minutes are equal to ' num2str(Hours) ' hours and ' num2str(Minutes) ' ...

1 month ago | 0

How to separate a string(1x1 cell) into a 1x4 cell
If the hex codes are always 8 characters, why can't you just pick off the characters you want? E.g., {result(1:8),result(10:17...

1 month ago | 1

how to generate a code for solving 2st order differential equations using improved runge kutta 4th order method
The posted code actually has a bug. Also it is almost set up properly for vector solutions, but not quite. Make these changes:...

1 month ago | 0

Computer crashed when calculating matrix (mixed with sparse and full) multiplication and summation
Remember that each element of the B*C result is simply the dot product of a row of B with a column of C. If that column of C ha...

1 month ago | 0

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Fast vector reshaping/permutation
Don't do the permute( ) operation. Just use pagemtimes( ) downstream in your code with the appropriate 'transpose' option. Thi...

1 month ago | 1

Can someone explain this Loop?
Of the numbers 1 ... 10 that get produced by the randperm( ) call, only three of them are less than 4: 1, 2, 3. 1 will cause n...

1 month ago | 0

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How to generate unique random integers between 1 to n (with no possibility of Sequence)
If 1:n is the only sequence you don't want, just use randperm(n) and reject the one case you don't want. I.e., if you get it the...

1 month ago | 0

How do solve four variables with one equation using Runge-kutta?
You have three state variables, namely v, lc, and z. But you only have code for updating v. You need code for updating lc and ...

1 month ago | 1

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A code and plot a graph for a projectile motion of a ball
Your main problem is that you don't have enough state variables. You have these two equations: x'' = 0 y'' = -g That's two 2...

1 month ago | 0

Converting Struct field to array
Does this do what you want? MyMatrix = vertcat(MyStruct.Field);

1 month ago | 0

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Trying to build a new nx4 array from an existing nx4 array using logical values
Assuming quatAB is a standard numeric matrix, use your logical variable for the first index and colon for the second index: m =...

2 months ago | 0

How do I combine a structure array into one structure
F = fieldnames(A); n = numel(F); C = arrayfun(@(i)vertcat(A.(F{i})),1:n,'uni',false); FC = [F';C]; B = struct(FC{:});

2 months ago | 0

Finding optimal value for x
You could try this function to get numeric values for local minimums: https://www.mathworks.com/help/matlab/ref/fminsearch.html...

2 months ago | 0

Using fprintf to save a matrix changes the order of my matrix
MATLAB stores 2D matrices in column order. That is, the numbers in your matrix are stored in memory in this order: 0, 1, 2, 3,...

2 months ago | 0

In addition to what @Image Analyst has written, I would advise turning this into a function with p1, p2, p3 as input arguments a...

2 months ago | 0

Difference between using single quotes ('xyz') and double quotes ("xyz") in formatspec
In MATLAB, single quotes ' ' are used to create char type variables, and double quotes " " are used to create string type variab...

2 months ago | 0

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Error in ode45 while doing numerical integration
The function handle you pass to ode45( ) needs to have a (t,y) signature. E.g., [t,y] = ode45(@(t,y) myode(t,gt,g), tspan, ic, ...

2 months ago | 0

How to multiply higher order matrices?
You may need to permute your arrays first to get your desired 2D slices in the first two dimensions. A = whatever B = whatever...

2 months ago | 2

Using matrix to index another matrix?
Does this do what you want: x = sub2ind(size(B),(1:size(A,1))',A(:,1),A(:,2),A(:,3)); Output = B(x);

2 months ago | 0

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Equivalent of c++'s NULL or python' s None in MATLAB
This will probably depend on how these are used downstream in your code and whether you have arrays of them to deal with. If th...

2 months ago | 1