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John D'Errico


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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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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...

5 hours ago | 0

| accepted

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...

1 day 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...

1 day ago | 0

| accepted

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;

2 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 ...

2 days ago | 0

| accepted

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...

3 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...

5 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...

5 days ago | 0

| accepted

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 ...

5 days ago | 0

| accepted

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 ...

5 days ago | 0

| accepted

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....

5 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...

5 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:...

5 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...

5 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...

7 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...

7 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...

7 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...

7 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...

7 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 ...

8 days ago | 0

| accepted

Answered
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 days ago | 0

| accepted

Answered
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 days ago | 0

| accepted

Answered
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 days ago | 1

| accepted

Answered
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,...

8 days ago | 1

Answered
Question about Anderson-Darling (adtest)
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...

8 days ago | 1

| accepted

Answered
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 days ago | 1

Answered
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 days ago | 1

Answered
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 days ago | 0

| accepted

Answered
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...

9 days ago | 1

| accepted

Answered
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 days ago | 0

| accepted

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