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John D'Errico


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Retired

5,236 total contributions since 2006

(Don't contact me. I won't answer questions.) A retired mathematician, numerical animalist, woodworker, bridge player.

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Answered
Find multiple values closest to zero
So, you are telling us that you know how to use a fragment like ind = find(diff(sign(values)))+1 ind = 14 24 27 ...

7 hours ago | 0

Answered
ASSISTANCE ON RUNNING RANDOM VARIABLES IN A FUNCTION
Note that a random variable is a well defined term in mathematics and statistics, though much of the time when I see someone use...

12 hours ago | 0

Answered
How to determine eigenvalues of symbolic matrix?
What form would you expect? Is there a reason why you expect the eigenvalues of a 4x4 symbolic matrix to be some nice pretty thi...

1 day ago | 0

Answered
fminunc gets first-order optimality of zero on iteration 0, does not find optimum
First, this appears to be a ONE parameter optimization. Do not use fminunc for that. Instead, us fminbnd. It will be more robust...

1 day ago | 0

Answered
symbolic toolbox problem ?
A strong possibility is you have overwritten/overloaded the stored value of pi. >> clear pi >> pi ans = 3.1415926...

2 days ago | 0

Answered
Find whether there is a trend over time or the data is completely random
This really is not a MATLAB question, as you have no idea how to compute what you want, and your question is too vague to have a...

3 days ago | 0

Answered
Weighted Least Square Fit regarding equal parts of the xaxis
You can't directly supply weights as an option to laqcurvefit. Better is to use lsqnonlin for this, since you return the residu...

3 days ago | 0

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Answered
Given that A is a sparse matrix, norm(A(i,:)) takes a very long time. Why and can one do better ?
You really don't want to use loops to do something like this. >> A = sprand(10000,10000,0.001); >> timeit(@() norm(A(1,:)))...

3 days ago | 0

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Answered
C = union( A,B ) is too slow. Is there any faster way given that A and B are ordered.
You could use unique. It would produce the same result, except that it will not be faster. A = sort(randi(1e7,1,1e6)); B = sor...

3 days ago | 0

Answered
Kindly help me to obtain the first four numerical solution of given trancedental equation "luck 1"
Have you not tried plotting it? It is so easy to say that you want the "first" 4 roots. >> vpa(subs(luck1,x,eps)) ans = -1.7...

4 days ago | 0

Answered
How to generate random numbers with constraints and different boundaries (for a high dimension)?
Neither of the choices on the FEX are directly a solution. randfixedsum fails because it explicitly assumes uniform bounds on th...

4 days ago | 0

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Answered
finding roots of equation in matlab
In general the roots of a 6th degree polynomial with unknown coefficients cannot be found in an algebraic form. At least not unl...

5 days ago | 1

Answered
Estimating parameter uncertainty with fminsearch
I think I am starting to understand what you are askng. One very good option is to use abs. I've been told I could use better ab...

5 days ago | 0

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Answered
How can i randomly insert 14 1's in a array of two thousand zeros?
A = zeros(1,2000); A(randperm(2000,14)) = 1;

6 days ago | 2

| accepted

Answered
How to solve this ode problem
Use none of them. This is NOT an ODE problem, except that you seemed to want to write it as such. It is certainly not something ...

6 days ago | 0

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Answered
Calculate the distance between a linear regression line and the data points
I am confident that what you are asking is an orthogonal distance, not the vertical difference, frequently known as the residual...

7 days ago | 0

Answered
How do I get the intersection function of 2 surfaces?
The intersection function will rarely exist as a "function". At best, it is an implicit function, thus a problem with solution l...

9 days ago | 0

Answered
ode,dsolve,spline,ode interp, differantial
You are not asking to do anything more than to integrate a spline, and perhaps to plot the result as a function of x. (You don't...

9 days ago | 0

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Answered
Integrating from polyint(p)
Sorry, but polyint cannot integrate a rational polynomial, and certainly not over an infinite region. Depending on the roots of ...

9 days ago | 0

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Answered
How to optimize matrix multiplication speed?
Do this: P = PHI*(P + Q)*PHI' + Q; While it may look exactly like the line of code you wrote, in fact, it is the same. Matrix ...

9 days ago | 0

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Answered
Algorithm to extract linearly dependent columns in a matrix
It is difficult to answer this. Consider a simple matrix: format short g A = rand(4,5) A = 0.73796 0.36725 0....

10 days ago | 0

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Answered
How can I create a function with random imputs? I have to create a function called tri_area that returns the area of a triangle with abse b and heigh h, where b and h are input arguments of the function in that order
I think you may be confused. I believe what is asked is for a function with ARBITRARY inputs, in the sense it can be called with...

10 days ago | 2

Answered
The accuracy on my LSTM deep learning neural network will not exceed 62.96%
You have shown no data, so we cannot truly say if you are doing something wrong. However, it sounds as it what you are doing is:...

10 days ago | 0

Answered
how can i get a number as an answer?
You got a number. :) I know, its net a very useful looking number. As s floating point sym, use vpa. vpa((23401992239682647381...

10 days ago | 0

Answered
why does similar code generate complex numbers?
What, for example, are the THREE cube roots of a negative number? We can find them all as solutions to the equation syms x xs...

11 days ago | 0

Answered
Is there a tool for drawing diagrams that connect equations?
I don't think there is a tool in MATLAB that will take a set of equations in arbitrary order, and then create this diagram. Yo...

11 days ago | 0

Answered
How can ı solve this constraint optimization problem?
Many things you can do, but since this is your homework, and there are already answrs posted, I'll just suggest a couple of thin...

11 days ago | 0

Answered
USING MEX TO SPEED UP THE CODE
As a counterpoint, there are some issues to consider. Much of MATLAB is already compiled code, at least in the hard working part...

11 days ago | 1

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Answered
help solving differential equations
I think you have multiple problems here, now that you claim to have the correct equation. DSOLVE finds an analytical solution to...

12 days ago | 0

Answered
Simplifying a algebraic or numeric expression to lowest possible power
The problem is, there are multiple solutions, because sqrt is not as simple a thing as you like. syms x >> y = sqrt(x.^2) y ...

12 days ago | 0

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