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John D'Errico


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Retired

5,349 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
Help with syms function. Unable to find explicit solution
Would you assume that every equation you write down hs an analytical solution? Why would you? T = 10; h = 20; g = -9.81; ...

1 day ago | 0

| accepted

Answered
how to separate variables of f(x,y)?
In a completely general sense, if you do not know IF the functions can be separated, then no it is probably impossible to do for...

3 days ago | 1

Answered
nonlinear equality constraint with symbolic variables
Numerical optimizers CANNOT use symbolic variables. That is, this is meaningless when using a tool like fmincon. syms t [1 16...

3 days ago | 0

Answered
linear regression in log-log scale
Sadly, while I wish the fitting tool would fit your data on log scales if that is how the axes are set, it does not. (That has a...

4 days ago | 0

Answered
Why multi objctive GA doesn't give identical answers?
First, many optimization problems have multiple solutions. Nonlinear problems often do. Second, there is no assurance that any ...

4 days ago | 1

| accepted

Answered
New to Matlab - need help with rearranging equation
There was NO error returned. It was a WARNING, that while you want to find a solution, none could be found. There are many thing...

4 days ago | 1

Answered
solve Equilibrium Position of Mass - Spring - Damped System
As Alan pointed out, you probably wanted to take the 2nd derivative of x there in your system, not the 20th derivative. The term...

5 days ago | 0

Answered
How do I express coefficient x, y, z using a, b, c, P0?
You can want to do anything you want. But unless you have a magic wand, that often fails. Here, you have ONE equation (3) that...

6 days ago | 1

| accepted

Answered
How to solve Ax=B with some knowns in x and B
This is a moderately complex question, because I'm not sure you fully appreciate the problem, and I am also sure this is not you...

7 days ago | 0

Answered
Row of a Pascal's Triangle using recursion
Simplest is to use conv. In terms of your code, I have no idea what you think the line PascalRow(1) = 1; does, but it does not...

10 days ago | 0

Answered
memory overflow with double factorial function
Recursive formulas like this always seem useful, but they are terrible in terms of coding, in terms of efficiency. You don't wan...

11 days ago | 0

| accepted

Answered
Unable to meet integration tolerances without reducing the step size below the smallest value allowed
Anytime you see this error message: "Unable to meet integration tolerances without reducing the step size below the smallest va...

11 days ago | 1

Answered
symbolic integration
No. You cannot first use a numerical integration to first integrate with respect to one variable, and THEN hope to use a symboli...

11 days ago | 0

Answered
Need fast quadrature method for use within root-finding routine
Way too late for this answer to be useful. In fact, way too late even for it to have been useful for me, when I had to solve the...

11 days ago | 0

Answered
Constrain a parameter in a fit?
Simple enough. You could do this using lsqcurvefit or lsnonlin from the optimization toolbox, which do allow bound constraints o...

11 days ago | 1

Answered
Why is lsqnonlin returning initial input values ?
lsqnonlin is not a function to optimize a scalar nonlinear function. Even though you could actually have written your problem in...

12 days ago | 0

Answered
Solving Equation Generated by pchipinterp method
The simplest way to do this is to use my SLM toolbox. x = sort(rand(1,20)); y = rand(1,20); spl = pchip(x,y); fnplt(spl) y...

12 days ago | 0

Answered
How to find the roots of the equraion f(x)=sin[sin(x)]+e^x=0
The simple answer is to know MATLAB syntax, and understand how to use a tool like fzero. So sin[sin(x)] may look better to you, ...

12 days ago | 0

Answered
How to find unstable solution
Your question about how to get two lines in one graph is a simple one. Use the command "hold on" between plots. That is... plot...

12 days ago | 1

Answered
3D shape approximation
An old question, answered here only to explain some aspects of the problem. It sounds as if you have an arbitrary shaped object...

13 days ago | 0

Answered
how to found bandes matrix
You have 5 non-zero bands. Use spdiags. Yes, you could use sparse. But since it is a banded matrix, use a tool to breate a bande...

13 days ago | 1

Answered
Behavior of a sequence
I won't do your homework for you. But I will offer some background to the solution. yn+1 =5/2 yn +yn-1 ,y0 =y1 =1 This is kno...

13 days ago | 0

Answered
Permanent A for any txt matrix
Actaually, probably NOT the determinant. The matrix permanent is sadly more computationally intensive than the determinant, whi...

14 days ago | 0

Answered
Ill-posed quadratic programing with linear inequality constraint
An old question, so my answer is completely irrelevant to Benjamin. Sorry about being late on this. But the solution is not that...

14 days ago | 0

Answered
reading elements of cfit
Easy enough. Consider the simple model: x = rand(10,1); y = rand(10,1); mdl = fit(x,y,'poly1') confint(mdl) So as you see, ...

14 days ago | 0

Answered
Constraints with fsolve
Fsolve CANNOT have constraints. The use of conditional statements inside your objective would often cause fsolve to fail to prop...

14 days ago | 0

Answered
can linprog handle discrete variables
linprog has NO ability to handle discrete variables. intlinprog, (introduced after this question was asked) can do so, in theory...

14 days ago | 0

Answered
Calculating model error
Even though you may THINK your data is good, the problem surely lies in your model. That it is a new device is not even relevant...

14 days ago | 0

Answered
finding vector from an equation
There is no solution. Except for possibly a trivial solution. And with some effort, I can prove that does not exist. norm(g(...

14 days ago | 0

Answered
Solving (non-linear equation) for a single unknown?
syms are a set of tools written to solve symbolic problems. fzero is a tool to solve numerical problems. The gray area between i...

15 days ago | 0

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