# James Tursa

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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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**Feeds**

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...

16 days ago | 33

| accepted

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.*...

2 months ago | 2

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...

3 months ago | 0

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?

4 months ago | 2

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...

4 months ago | 0

| accepted

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 ...

4 months 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...

4 months ago | 2 answers | 0

### 2

answersRank 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...

4 months ago | 0

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...

5 months ago | 1

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...

5 months ago | 1

| accepted

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...

5 months ago | 1

| accepted

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...

5 months ago | 1

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...

5 months ago | 0

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).'

5 months ago | 0

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...

5 months ago | 0

How to convert dates into Julian dates?

Based on your comment that you are expecting numbers in the range of 273,287,298, etc., if what you are after is actually "day ...

5 months ago | 0

How to create for loop for calculating euclidean distance of a matrix?

Does pdist() do what you want: https://www.mathworks.com/help/stats/pdist.html?s_tid=doc_ta

6 months ago | 0

converting 3d matrix into a cell array

x = rand(1001,259,259); result = arrayfun(@(k)squeeze(x(k,:,:)),1:size(x,1),'uni',false); size(result) size(result{1}) But, ...

6 months ago | 0

How to implement the Central Difference method integrator for a two body problem?

You have: altitude tangential velocity If you just want the orbital period, you can calculate as follows using the Vis-Viva e...

6 months ago | 0

Can multiple versions of MATLAB be installed on the same Windows PC using the same license number for code compatibility?"

Multiple MATLAB versions can be installed on the same machine as long as your license permits it. Both can even be run simultan...

6 months ago | 0

How to calculate the angle between two 3D vectors?

See a discussion here (includes a tiny angle example): https://www.mathworks.com/matlabcentral/answers/101590-how-can-i-determi...

6 months ago | 1

Double precision: Why does fprintf print "extra" wrong non zero digits?

The "extra" digits that look incorrect to you are simply the result of doing an exact conversion of the actual floating point bi...

6 months ago | 1

| accepted

What does MATLAB actually do when switching precisions?

When converting from IEEE single to double, the sign bit is retained, the exponent bits are adjusted to match the same exponent ...

6 months ago | 2

I want to solve ODE for a complex systems in a rk4 method

Just turn all the y( ) stuff into row or column vectors. E.g., suppose we use column vectors, then something like this ... y = ...

6 months ago | 0

| accepted

quat2angle / atan2 strange quadrant change when calculating angle

You don't show us your code, but in general I would note that angle changes like this are sometimes the result of whole quaterni...

7 months ago | 0

Active rotation with quaternions: from initial orientation given with Euler angles get the new orientation after an active rotation described by the qr quaternion.

Yes, for your convention q' = q * qr is mathematically correct. But note that this formula only works for certain quaternion co...

7 months ago | 1

| accepted

Question

Conjugate of Symbolic Root doesn't change anything

Reference question first asked here: https://stackoverflow.com/questions/78010011/matlab-bug-with-root-and-conj Basically, the...

7 months ago | 1 answer | 1

### 1

answersparse matrix entries are not displayed correctly

I finally finished my sparse matrix integrity checker. You can find it in the FEX under the name SAREK (I think you will be able...

8 months ago | 0

the tranpose of transpose doed not equals the original matrix

I finally finished my sparse matrix integrity checker. You can find it in the FEX under the name SAREK (I think you will be able...

8 months ago | 2