James Tursa

Last seen: Today | Active since 2007

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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
Plots saved as JPEG look awful. How to improve?
You might also explore export_fig from Yair Altman, found here: https://www.mathworks.com/matlabcentral/fileexchange/23629-expo...

1 dag ago | 0

Answered
need to vectorize efficiently calculating only certain values in the matrix multiplication A * B, using a logical array L the size of A * B
You can try this naive mex routine. Not optimized at all for cache hits or patterns in L. Might be faster to transpose A first, ...

22 dagen ago | 1

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Answered
ode45 code for 2 body problem
Your system has an initial non-zero total linear momentum. Recall that the 2-Body Problem has a constant center of mass motion ...

23 dagen ago | 0

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Get total number of leap seconds relative to gps time
To convert a GPS timestamp to a UTC time, use the UTCLeapSeconds time zone which automatically accounts for leap seconds in the ...

4 maanden ago | 0

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How to use datetime with leap second strings?
@Peter Perkins Thanks for the reply. My comments ... "... I'd be curious to hear where you are getting timestamps that honor l...

4 maanden ago | 0

Answered
How to preserve nanosecond precision in datetime calculations (for large numbers)
This question already has an accepted answer, but I would like to add my observations on this topic. datetime: Internally hold...

4 maanden ago | 0

Question

How to use datetime with leap second strings?
Suppose we have the following date time string: ds1 = "30-Jun-1972 23:59:59.5"; You can convert that to a datetime easily: da...

4 maanden ago | 3 answers | 0

3

answers

Answered
Why Is Colon Operator Not Equivalent To linspace Command?
The short answer is that the algorithms are different. In the first place, 0.08 cannot be represented exactly in IEEE double pre...

4 maanden ago | 3

Answered
C++ Mex function being passed a MATLAB class object
mxDuplicateArray( ) does indeed create deep copies ... or at least it used to. Not sure why that would have changed. There migh...

4 maanden ago | 1

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Answered
Error using mex, building with 'MinGW64 Compiler (FORTRAN)'
FYI, you should never use literal constants in a Fortran API call, because you can't be sure whether the literal integer(4) or i...

5 maanden ago | 1

Answered
How to pass a Matlab function handle to C-Mex Code
To use a function handle in a mex function with C array as an input to the function handle, you can use mexCallMATLAB( ) with th...

5 maanden ago | 2

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Answered
Kalman Filter Velocity data looking too similar to position data
Your velocity vf and position rf calculations as shown represent "change" over dt, not current value. Think about it. If you had...

5 maanden ago | 0

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Answered
Is giving a space after comma in functions the convention?
A MATLAB specific thing that is somewhat related is that spacing is important in concatenation. E.g., the following look similar...

6 maanden ago | 1

Answered
My Numerical Solution doesn't align with the exact solution
Assuming your state is [vc,vc'] in that order, then it appears your initial conditions are backwards and should be this instead:...

6 maanden ago | 1

Answered
How can I find index of element in array?
To find the index of a specific integer value (without roundoff error) in an array of integers, use the "find" function and == o...

6 maanden ago | 33

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Answered
Order terms in symbolic poly converted to string
Brute force if you need the string for some reason? syms x ex = taylor(exp(x),order=3) [C,T] = coeffs(ex) terms = fliplr(C.*...

8 maanden ago | 2

Answered
How can we convert a datetime into a string that represents a Unix timestamp in nanoseconds?
Another workaround that avoids the lossy duration type issues and doesn't need the messy struct solution for this particular cas...

9 maanden ago | 0

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Write a function called freezing that takes a vector of numbers that correspond to daily low temperatures in Fahrenheit. Return numfreeze, the number of days with sub freezing
Hint: Is it freezing when the temperature is above 32 or below 32? And what have you coded?

10 maanden ago | 2

Answered
How to do differentiation in Matlab
Are you just asking for piecewise linear differencing for derivative calculations between the points? E.g., THT = 0:12:360; L...

10 maanden ago | 0

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Answered
Matlab got this wrong: Limit as n goes to infinity: (1+(i/n))^(n^2). Matlab says it's exp(2), which is wrong. Pls confirm.
I have been looking at this for a couple of days now and have finally convinced myself that this limit doesn't exist and MATLAB ...

10 maanden ago | 0

Question

Duration type doesn't preserve seconds accuracy
I've been working on some time conversion routines and ran into an issue I didn't expect. Basically, the duration type doesn't p...

10 maanden ago | 2 answers | 0

2

answers

Answered
Rank value matrix from 3d Matrix
Might be easier to permute first so that your 2D matrices are in the first two spots. Then simply use sort() to get the rank ind...

10 maanden ago | 0

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Error with matrix calculation
We don't have all the variables necessary to run your code, but guessing that maybe you need element-wise divide instead of matr...

10 maanden ago | 1

Answered
Unable to resolve the name 'half.typecast'
half is an opaque data type in MATLAB, not a regular numeric type like double and single. I tried to get TMW to change this to a...

11 maanden ago | 1

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Answered
What does it mean "/Multiple" after variable name in *.mat file?
If the file is written by a 3rd party tool, it is probably written in uncompressed format. In that case, and if the /Multiple is...

11 maanden ago | 1

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Answered
Having issues writing matrix to a binary file.
@Rikin You forgot to read in the sizes. You only read in the double data. The two int32 variables at the front obviously were pa...

11 maanden ago | 1

Answered
How to write a matrix with elements 10,30,10
Use brackets M2 = [10,30,10]

11 maanden ago | 0

Answered
an ode with arguements
Create a new function handle with your extra stuff. E.g., mufunT = @(eta,f) mufun(eta,f,guessT) [eta, f] = ode45(mufunT, [lins...

11 maanden ago | 0

Answered
Column to matix In matlab
Depends on how your data is currently stored. Suppose the data is currently in a vector v. Then matrix = reshape(v,50,10).'

11 maanden ago | 0

Answered
How do I process a string class in a mex function?
Strings are opaque objects (like classdef) and there are no API functions to get pointer access to the data areas. I am unaware...

11 maanden ago | 0