# 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**

Is it possible to process the sparse matrix faster with vectorization instead of for loop?

You need to re-evaluate how you are doing things. In the first place, you have the Euclidean calculation wrong. It should be thi...

3 giorni ago | 0

How to exchange data between two C++ MEX files

Your current scheme is not foolproof. How does the 1st mex function know when it is safe to unlock and clear memory? How does th...

3 giorni ago | 0

| accepted

How to solve Lc=y without backslash operator?

First, I am assuming there is a typo and the system you are solving is Ly = c, not Lc=y. Second, you made a good start by writi...

6 giorni ago | 0

I am using euler's method to solve a differential equation, but when I run the code it doesn't plot.

Take a look at these lines: t0=0; %start time t1= 500; %finish time dt = 100000; Your stepsize is much larger than the total...

8 giorni ago | 1

| accepted

Accessing struct using C library always NULL

Typically, it is best just to post your code so we can see exactly what you are doing, instead of posting a description of your ...

8 giorni ago | 1

| accepted

Errors while trying to setup equation for root finding.

Did you mean multiply by the "a"? x_pdo = z_pdo/(1 + a*(k_pdo - 1)); x_water = z_water/(1 + a*(k_water - 1)); x_glycerol = z_...

8 giorni ago | 0

How do I access a field from a function's input?

Assuming you are passing in a character string for freq, use this syntax: output = myStruct.(freq);

10 giorni ago | 0

| accepted

How can I obtain the T and Y for R Runge Kutta method?

The first version has an error. This line: k3=h*feval(f,T(j),Y(j)); should be this instead: k3=h*feval(f,T(j)+h/2,Y(j)+k2/2);...

16 giorni ago | 0

How to solve array indices error?

x1 = 0*ft; : distance1=sqrt((x1-x2)^2+(y1-y2)^2+(z1-z2)^2); : sp = distance1(x1,y1,z1,dx,dyv(i),dz); % incident di...

26 giorni ago | 0

Solving ODE using Euler Method and 4th Order Runge Kutta Method

You pretty much have the Euler scheme worked out, so I will help you with a vector formulation. Take this code: for i=1:n ...

circa un mese ago | 0

| accepted

Problem finding sum of array using vectorization

The first element of x is 1, so that element produces 1/(1-1) = 1/0 = inf in the second line. You need to rewrite that second li...

circa un mese ago | 0

Multiplication of large matrix with its transpose

The fastest way is to simply write it as A * A', because MATLAB will see that the operands are the same and call a special multi...

circa un mese ago | 0

Solving ODE in MATLAB using Runge-Kutta method of order 4

Why aren't you using this to update z: z(i+1) = z(i) + (1/6)*(l1+(2*l2)+(2*l3)+l4);

circa un mese ago | 0

Why is the string type not implemented as standard type?

All of the standard full numeric types as well as char and logical are implemented as simple rectangular data arrays. The string...

circa un mese ago | 1

how to print randomly selected column?

Shouldn't that be size(data,2)? Also, generally you should be using string comparison functions for the tests, not the == opera...

circa un mese ago | 0

NaN shows up in matrix when solving my ODEs, how can I fix this?

"All of my matrices I am solving for have NaN after the third time line. How do I solved this issue?" Set up a breakpoint somew...

circa un mese ago | 1

| accepted

Mean of multidimensional array

Doesn't mean(mdar,3) do what you want?

circa un mese ago | 0

| accepted

Function Error: Array indices must be positive integers or logical values.

When you have parentheses appear on the left hand side of an assignment like this: v(ro,ri) = (sqrt(m/(ri)))*((1/sqrt(R))-((sqr...

circa un mese ago | 1

| accepted

MXCREATEDOUBLEMATRIX memory overflow error

Rather later for an Answer, but here goes anyway: You should never use literal integers for API calls, because you can't be sur...

circa un mese ago | 0

Convert unsigned integer to decimal

Not sure what the real question is here. Does one of these do what you want? int1 = uint32(hex2dec('9d900000')); int1 = uint32...

circa un mese ago | 0

convert integer to bytes

Depending on what you are doing downstream with this, you can use the typecast( ) function. E.g., bytes = typecast(my_integer,'...

circa un mese ago | 0

| accepted

Selecting multiple different rows in a 3D matrix

You can use a vector for the indexing. E.g., x = matrix(:,:,[2:16,24:48]); Does that, or something like that, do what you wan...

circa un mese ago | 0

Using a variable vector in a loop

Suppose you store the column vectors in a matrix called V. Then vk would simply be V(:,k). And if the uj are stored in a matrix...

circa 2 mesi ago | 1

| accepted

Fortran code in Matlab

I'm trying to figure out the purpose of the backslash \. If this was the last character in the format statement then I would ass...

circa 2 mesi ago | 0

Assigning mxUint16 variable to plhs[0]

You cannot attach native C/C++ memory to an mxArray. The MATLAB API "mxSetEtc" functions check to see that the memory addresses ...

circa 2 mesi ago | 0

| accepted

How to separate a vector into two different vectors?

Others have already pointed out better ways of doing this. But to answer your question as to why your current code is not workin...

circa 2 mesi ago | 1

Nested "For Loop" Array Size

To keep the indexing the same, just use the top value from the loops. E.g., DataArray = nan(300,50,100,numel(inputValsY3)); No...

circa 2 mesi ago | 0

| accepted

convert value from radian form to degree form

If you have values, then just number_in_radians = number_in_degrees * (pi/180); If you are working with trig functions, note t...

circa 2 mesi ago | 0

Calculate taylor series using while loop

Looks like you are planning to use the identity ln(5) = ln((1/5)^-1) = -ln(1/5) and then use 1/5 as the x in the Taylor Series e...

circa 2 mesi ago | 0