# James Tursa

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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**Content Feed**

What does A(2:4) = [ ] do if A is a 3x3 matrix?

This is linear indexing. Even though the variable is a 2D matrix, MATLAB allows you to index into it using only one index. The l...

5 dagen ago | 1

error using function code

Create a file called lettergrade.m somewhere on the MATLAB path (e.g., in your working directory) edit lettergrade.m Copy all ...

5 dagen ago | 0

dynamic naming of structures

Would it be acceptable to use x as a dynamic fieldname instead of the top level variable name? E.g., v.(x).a v.(x).b

5 dagen ago | 1

How can I define an array of sparse matrix? (both for GPU and CPU)

For CPU, you can use the ndSparse submission by Matt J on the FEX: https://www.mathworks.com/matlabcentral/fileexchange/29832-n...

5 dagen ago | 0

numerical integration with recursive trapezoid rule

Some issues are immediately apparent. First, you don't reset S=0 inside the while loop. Isn't S supposed to contain only the a...

5 dagen ago | 0

Store every N columns in a Matrix to a new Matrix

Don't create a bunch of new matrices with hard to use names downstream in your code. Instead, simply reshape your matrix and the...

10 dagen ago | 0

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MEX file always crashes when I run it

In the MATLAB code you have this: np=single(np); Then inside the Fortran gateway routine you have this: mwPointer xr, yr, n ...

10 dagen ago | 0

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How can I reshape a matrix this way

a=[-0.26,0.23,0.033,0.1,-0.39,0.30;0.30,-0.39,0.10,-0.26,0.03,0.23;-0.03,-0.13,0.16,0.33,-0.16,-0.16] b=[-0.26,0.23,0.033;0.1,-...

16 dagen ago | 0

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Matlab while loops with equations

You should probably go through the online tutorials for learning MATLAB. But I will give you an outline to get started: toleran...

17 dagen ago | 0

i need to find error in code because I it's increasing but it should be decresing

You need to use all the derivatives at the first point to propagate for the initial guess at the second point. I.e., these lines...

18 dagen ago | 0

t = 2 s, i = √−1, and 𝜔=120π rad/s. Evaluate the following using MATLAB? Hint: exp(n) is used in MATLAB to evaluate en. (a) e−2𝑡𝑐o𝑠 (𝜔𝑡)

I am guessing that the original expression shown is supposed to be interpreted as: Then take the hint at how to evaluate the ...

ongeveer een maand ago | 0

Why is my projectile motion code only working at certain input angles.

Drag depends on current velocity, not initial velocity. So you need to recalculate V at each step. E.g., Vx = Vx_new; Vy = Vy_...

ongeveer een maand ago | 0

Sine equation in Euler Method ODE

You've only got one scalar differential equation, so I don't understand why you think you need two variables x and y along with ...

ongeveer 2 maanden ago | 0

subtract matrix from vector

Just learn how to use indexing and element-wise operators. From your language, here are the pieces: subtract - the first thre...

ongeveer 2 maanden ago | 0

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How can I create arrays with different names using loop?

Don't embed numbering into the variable names. This will make the variables hard to use downstream in your code. Use cell arrays...

ongeveer 2 maanden ago | 0

How to subtract each column of a matrix from a column vector?

Just do a usual subtraction and let MATLAB implicit expansion kick in: M = your matrix v = your column vector result = v - M;...

ongeveer 2 maanden ago | 0

Simple mex file crash?

You need to create the output variable yourself. plhs[0] doesn't exist until you create it, thus this line crashes: outData = m...

ongeveer 2 maanden ago | 0

Simulating Projectile with Matlab

You don't show us both methods (with and without drag) so we can't compare them. I presume you simply set k=0 for the case witho...

2 maanden ago | 1

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Matlab simulation for planet motion

The initial condition for position and velocity need to be outside the loop, prior to loop entry.

2 maanden ago | 1

| accepted

Vector ODE solution is not periodic/ as expected

This index 4 dxdt(4) = -DU^2* x(3)/sqrt(x(1)^2+x(2)^2+x(3)^2)^3; needs to be index 6: dxdt(6) = -DU^2* x(3)/sqrt(x(1)^2+x(2)^...

2 maanden ago | 0

| accepted

How to compile a Fortran subroutine by using the MEX engine

It looks like you are taking input, calling a MATLAB function, and getting output from that function. I still say it would be ea...

2 maanden ago | 0

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How to create Matrix [1 2 3 4; 2 4 6 8; 3 6 9 12; 4 8 12 16] without using loops or any functions using loops?

n = 4; % whatever result = (1:n) .* (1:n)' % use implicit expansion row .* column

2 maanden ago | 2

| accepted

Vectorising Multiplying each column from a matrix with a square matrix and the tranpose of this column

If you need the same column on each side of the multiply, then maybe this: result = sum(h'*Pn.*h',2);

3 maanden ago | 1

Problem in using mxSetPr with USHORT

To attach pointers of type other than double to an mxArray, you can use the mxSetData( ) function as Jan suggests. In your case ...

3 maanden ago | 1

Beginner coding; my second, simpler approach at trying to make all elements distinct.

FYI, to generate random integers you can use the randi( ) function instead of ceil(value*rand( )): https://www.mathworks.com/he...

3 maanden ago | 0

How to make a "page transpose" in a 3D matrix without using the function pagetranspose?

Mtranspose = permute(M,[2 1 3]);

3 maanden ago | 2

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How to multiply an inverse matrix (nxn) by an array (nx1) using for loop

Not sure why you have a for-loop at all. Maybe you can explain this. If you just want to multiply the explicit inverse by a vect...

3 maanden ago | 0

Adding numbers to an array

You don't really need both h and hnew. Just use h and some indexing. E.g., h = zeros(1,45); % allocate expected result k = 1; ...

4 maanden ago | 0

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rounding issues in matlab, need to force values to 0

Instead of if abs(y1)< 1e-6 y1=0; end try y1(abs(y1)<1e-6) = 0;

4 maanden ago | 2

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why will the area only work for the circle and not the other shapes

To compare strings, do not use the == operator which does an elementwise compare. Instead, use a function meant for comparing st...

4 maanden ago | 0