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# John D'Errico

### Retired

5.226 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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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...

alrededor de 11 horas ago | 0

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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...

1 día ago | 1

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...

1 día ago | 0

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

2 días ago | 2

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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 ...

2 días ago | 0

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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...

3 días ago | 0

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...

5 días ago | 0

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...

5 días ago | 0

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

5 días ago | 0

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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 ...

5 días ago | 0

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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....

6 días ago | 0

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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...

6 días ago | 2

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:...

6 días ago | 0

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...

6 días ago | 0

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...

7 días ago | 0

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...

7 días ago | 0

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...

7 días ago | 0

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...

7 días ago | 1

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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...

8 días ago | 0

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 ...

8 días ago | 0

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Install 2 instances of Matlab on the same PC
Yes, and no. I frequently have several old versions of MATLAB on my computer. Walter has many as I recall. The only issue is if ...

8 días ago | 0

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Is there any method to calculate the inverse of matrix which changed a few values?
Bruno is correct in how to solve the problem, and also SOME of the issues with it. If you use this tool multiple times, the floa...

8 días ago | 0

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wrong differential equation solution
Sorry. I don't know what you did incorrectly, but here is what I see. syms y(t) yalpha = (1/80)*(36*exp(-t) + 125*sin(t) -3*...

8 días ago | 1

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How to limit calculation precision?
There are only two standard choices in MATLAB for floating point computations, and two ways to get round the problem. That is,...

9 días ago | 1

Not using adtest. Like the Ford Model T, which Henry Ford sold in any color as long as the color you wanted was black, adtest te...

9 días ago | 1

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Problem of ``sprandn'': the number of nonzero elements is inconsistent with density
Bruno has already explained why sprand/sprandn fail to produce the requested density of arrays. So this answer is here only to a...

9 días ago | 1

How to place a number (1) in a random position in Line 1 in a matrix of zeros?
M = zeros(10,10); M(1,randi(10)) = 1; However, if you had no idea how to solve a basic problem of matrix indexing, you REALLY ...

9 días ago | 1

find the std of each parameter after lsqlin
There are some issues that make this a little problematic. The main issue is if lsqlin finds itself butted up against a boundary...

9 días ago | 0

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How do I remove the z variable in the polynomial equation?
What you don't understand is that IF you did what you want, the polynomial will become diffcult to use and difficult to evaluate...

10 días ago | 1

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Can one run fminsearch on grids?
No. fminsearch presumes a continuously valued function, defined everywhere. You CANNOT use it to solve discrete problems. And ev...

10 días ago | 0

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