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John D'Errico


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Retired

5,362 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
2010 won't activate
The odds are good that your new computer will not run that old a release. 2010 is pretty old as things go. Check the system requ...

1 day ago | 0

Answered
How to work with a matrix close to singular in MATLAB ?
Sorry, but no magic exists. This is why numerical linear algebra exists as an area of mathematics, and why courses are taught in...

2 days ago | 0

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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 ...

4 days 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...

4 days 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...

4 days ago | 0

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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...

5 days 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 ...

5 days 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...

5 days ago | 0

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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...

6 days ago | 0

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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...

8 days ago | 0

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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...

8 days ago | 0

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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 ...

8 days 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; ...

11 days ago | 0

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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...

12 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...

12 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...

12 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 ...

13 days ago | 1

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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...

13 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...

14 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...

15 days ago | 1

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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...

16 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...

19 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...

20 days ago | 0

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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...

20 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...

20 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...

20 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...

20 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...

21 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...

21 days ago | 0

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