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John D'Errico


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Retired

5 360 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 solve 3 functions in 4 variables
What you show is NOT the answer. It is AN answer. 3 equations with 4 variables is called an underdetermined problem. There is ...

environ 18 heures ago | 0

Answered
Error solving three equations in three unknowns
syms a b c Tan = -b - 2 == 0; Man = c + 1 == 0; Lan = a + b - 3*c - 1 == 0; [av,bv,cv] = solve(Tan,Man,Lan,a,b,c) This is a...

1 jour ago | 0

Answered
Numerical Approximation of Fisher Information Matrix
You cannot perform numerical differentiation? At the very least, you can use tools for numerical differentiation from my derives...

1 jour ago | 0

| accepted

Answered
Finding an analytical fit for a multi-dimensional function
Read again what Walter has said. There is much to learn for you. You might also look at some of what is found in this post, whi...

2 jours ago | 0

Answered
optimization with multivariable and constraint
Sorry, but this seems just plain silly. You are way overthinking things. The new point P3 lies at the midpoint of the straight ...

2 jours ago | 0

Answered
How to create a 6 dimension array in Matlab and store values in it
It very much depends on what you want to do with that data. But I think you are looking for a very inefficient way to store your...

2 jours ago | 0

Answered
How to write the codes for this gamma function?
Easy, peasy. Although since you are using gamma as a FUNCTION, it is a REALLY bad idea to use beta, another closely related spec...

3 jours ago | 0

| accepted

Answered
Recursive function to reverse a vector
Hmm. Suppose you strip off the last digit of the vector on each pass? Can you do that? You already know how to find the last ele...

5 jours ago | 0

Answered
I want to make a recursive function that sums all the digits in a number
The "last" digit? A little ambiguously stated. In the number 12345, is 5 the last digit you are asking about? It looks like you...

5 jours ago | 0

Answered
How can I interpolate a screw surface?
Is this a single valued function of x and y? Or x and z, y and z? No. Is this a function over some contiguous convex region in ...

5 jours ago | 0

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; ...

8 jours 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...

9 jours 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...

9 jours 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...

10 jours 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 ...

10 jours 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...

10 jours 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...

11 jours 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...

12 jours 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...

13 jours 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...

16 jours 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...

17 jours 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...

17 jours 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...

17 jours 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...

17 jours 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...

17 jours 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...

18 jours 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...

18 jours 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, ...

18 jours 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...

18 jours ago | 1

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