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# James Tursa

##### Last seen: Today
3,669 total contributions 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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Function takes as input two nonempty matrices A and B and returns the product AB
This is a matrix multiply, so you need to keep the rows and columns of the inputs separately. E.g., [NRowsA,NColsA] = size(A);...

2 days ago | 0

Roll a die until n consecutive rolls have the same value
You made a good start, but it might help to change your inner while loop exit condition to be exactly what you are looking for ....

2 days ago | 0

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Solve function give 2 answers when there should be 1.
For a generic orbit problem, i.e. an ellipse, there are always going to be two places on the orbit path with the same r value (e...

7 days ago | 0

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MatLab While loop indexing?
Add a counter to your loop. Initialize the counter to 0 and add 1 to it within the loop. E.g., counter = 0; % other stuff w...

7 days ago | 0

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Extracting a submatrix based on conditions on first columns of a big matrix
BigMatrix = your big matrix BigMatrix1 = BigMatrix(:,1); % 1st column x = BigMatrix1 > 527 & BigMatrix1 < 580; % logical index...

7 days ago | 0

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Can someone help me figure out what is wrong with my function c1 = ult_trid(m,b) ??
d is a 4x1 vector and you are trying to access the d(4,4) element, hence the error.

13 days ago | 0

Question about numerical integration for cos vs cosd
By hand: int cosd(theta) = int cos(theta*pi/180) = sin(theta*pi/180)*180/pi Integrated from 0 to 15 degrees: sin(15*pi/180)...

13 days ago | 2

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Error: File: d3.m Line: 7 Column: 10 Invalid use of operator.
Looks like you are missing some variable names and some matching parentheses in this line: scatter((:,1)),(:,2)),'o')

14 days ago | 0

I would assume from the equation image that the exp( ) stuff maybe should be outside of the sin( ) stuff. E.g., f = 2.*x.*sin(...

14 days ago | 0

How to create multiple matrices with different sizes without a loop?
You will either need to use loops, or hide the loops behind a function call (e.g., arrayfun): result = arrayfun(@(x)randi([0 x]...

15 days ago | 0

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I need help solving a equation with the Runge-Kutta-Fehlberg adaptive step size method using ode45.
For Problem 2 and Problem 3, you should not be looping over any variables. You simply have a derivative function that you pass ...

15 days ago | 0

Wrapper to run 32-Bit mex files on 64-Bit MATLAB
32-bit mex files are not standalone code. They interact with 32-bit MATLAB library code which interacts with the 32-bit MATLAB ...

15 days ago | 0

Taylor series for sin(x) doesn't give the right answer above 34 radians
The larger x is, the more cancellation error you are going to get with the intermediate sums. It would be best to reduce the ra...

16 days ago | 0

code for eulers method help
This needs to be outside of and prior to your loop, and r needs a multiply operator: f=@(y)r*(1-(y/L))*y-((p*y^2)/(q+y^2)); Th...

16 days ago | 1

minutes to hour and minutes
Make mins a column vector, or use mins(:) in your function handle.

17 days ago | 0

syntax error using complex loops
Did you mean while c <= 19 For loops should be looping over a fixed number of iterations, not a logical condition. While loop...

17 days ago | 0

Create Array that reorders given values to have smallest first and largest last while maintaining the rest of the array.
That 2nd loop needs to run in reverse order. You need to bubble that smallest number which might be near the back all the way t...

17 days ago | 0

Need helping creating and solving for this equation: f(t)=4- t^2 e^(-3t)
Here is a basic outline to get you started: n = 100; % Number of elements t = zeros( you fill this in ); % create an t vector ...

19 days ago | 0

How can I use a for loop to create new variables?
You might consider automatic array expansion. E.g., look at this result: t = 0:0.01:10; % row a = [0.1 1 3]'; % column y = e...

22 days ago | 1

Can someone convert this to matlab code?
So, you don't need any loops for this. Just use the automatic array expansion feature. E.g., take a look at what happens with ...

22 days ago | 0

Two variables need to be connected to one struct variable.
What about something like this: Results.First_Name = first_name{target}; Results.Last_Name = last_name{target}:

22 days ago | 0

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How would I write the function of f(x)=sin(x)*exp(-x/10)
The multiply. E.g., f = @(x) sin(x) .* exp(-x/10); You don't need it on the divide because you are dividing by a scalar.

22 days ago | 1

Error using ^ (line 51) Incorrect dimensions for raising a matrix to a power. Check that the matrix is square and the power is a scalar. To perform elementwise matrix powers, use '.^'.
This is often caused by using a matrix or vector in an equation when you thought you were using a scalar. E.g., take these lines...

22 days ago | 0

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Try reading and keeping the type as uint64 (using the *) instead of converting to double: word = fread(fid,1,'*uint64');

22 days ago | 0

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mex, error C3861: "mxGetDoubles": Cannot find the identifier, "mxGetUint8s": Cannot find the identifier ？
Those functions are for the R2018a memory model API. For that, you need to add the -R2018a option flag: mex myfile.cpp -R2018a...

23 days ago | 0

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Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.
You are missing an ending parenthesis, and also you probably need to use element-wise multiply: u3 = exp(-0.89*t) .* (1.75*cos(...

23 days ago | 0

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Solving a nonlinear ODE
Step 1: Solve your ODE for the highest order derivative, in this case Rdoubledot (on paper) Rdoubledot = stuff (you figure thi...

26 days ago | 0

Computational Complexity of matrix multiplication
This question is perhaps more involved than it looks on the surface, because by default MATLAB doesn't store the imaginary part ...

26 days ago | 0

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