# John D'Errico

### Retired

DON'T contact me. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting. A retired mathematician, numerical analyst, woodworker, bridge player.

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**Content Feed**

Modification in besselk (Modified Bessel fn of 2nd kind order zero)

Simple answer - No. Utilities like this, erf is another excellent example, that while they can be defined in terms of an integr...

7 hours ago | 0

| accepted

I am trying to solve for w using determinants

Why do you think there is a problem. We can shorten the coefficients of Z a bit, just to look at what is happening. vpa(Z,3) a...

23 hours ago | 0

Is there a way to get the same results for linprog & fmincon given the same optimization problem?

Well, NO. You cannot insure exactly the same solution will arise from both solvers. I can think of several ways for the two solv...

1 day ago | 1

| accepted

Does anyone know how to add the legend?

x = rand(1,5); y1 = x + 2; y2 = x*2; plot(x,y1,'ro') hold on plot(x,y2,'bs') legend('+2','*2') Really, pretty basic. In...

1 day ago | 0

what is the difference between assigning with and without range?

Yes. There is a difference, and a fundamental one. In the first case, the assignment a=b COMPLETELY replaces a. The variable is ...

1 day ago | 0

Help solving a nonlinear function

I don't know what it means when you call something an equation that varies in a loop. This is certainly not a PHD level rabbit h...

5 days ago | 0

Solving for different thetas in an equation.

You CANNOT solve for both theta1 and theta2 in a single equation like that. (I assume you meant a single equation, because you h...

7 days ago | 0

How does this code support in carparking slot identification?

Out of context, this code is meaningless. It has absolutely nothing to do with the question you have asked about. And that was e...

7 days ago | 0

Project Euler: Problem 11

As far as why it failed test case #3, perhaps you need to write better, more efficient code. The code you wrote will be a bit of...

8 days ago | 0

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Integrate Acceleration to velocity, wrong plot

I would suggest your problem may be a simple one. When you integrate a function, there is a constant of integration, which is ...

8 days ago | 0

skewness and kurtosis of a weighted distribution

Sorry for being late to the party, but I had to answer this question once I saw an answer posted that does not actually help. T...

9 days ago | 1

WHAT IS THE SOLUTION FOR

Why? Is there a problem? Are you worried that your code is taking 1 millisecond longer to execute in this case? My point is, th...

11 days ago | 1

| accepted

FORTRAN POPPAR Equivalent in Matlab

The obvious answer is the simple answer... sum(dec2bin(I) - '0')

16 days ago | 0

| accepted

ode45 solving a differential equation that has no solution for given boundary conditions

So, you formulated a 2nd degree ODE. Converted it as: syms x(t) eqn = diff(x,2) + x == 0 [V] = odeToVectorField(eqn) M = m...

16 days ago | 0

| accepted

manually-written floor function code for rounding non-integers

If you want a mathematical expression, WRITTEN in MATLAB (where it will not have been written in the actual code) this could wor...

16 days ago | 2

| accepted

Questions on "Ordinary kriging"

As Jan told you, vstruct is provided by variogramfit. Where can you find that code? You need to download variogramfit, also prov...

16 days ago | 1

Rescaling curves by a factor to a single curve

You are looking to fit these curves using some nonlinear model. But you have not even said what model you want to use, just that...

17 days ago | 0

Can I solve a constrained optimization of general form of algebraic equation using matlab?

The problem is, even a simple function as you have written is is not as simple as you think. This is a problem of understanding ...

19 days ago | 0

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Problem when testing long decimal numbers

The problem is merely your understanding of floating point numbers and the methods used to store them. MATLAB uses only 52 bina...

20 days ago | 0

| accepted

Solving Ax=b but only for the values in some rows of x

We are given a problem where A is a large sparse matrix. We wish to compute the solution for the problem A*X == b where b ...

21 days ago | 1

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Optimization solvers change their performance in different programming languages?

No. The language makes NO choices. It does not prepare the problem differently. A language is not in itself sufficiently intelli...

21 days ago | 0

I have a problem with my code, it works fine but the results it isn't correct because the code is not compatible with the equations .. description below

This is one of those questions that tend to languish unanswered on the site. Why? Because you just say that your code does not w...

22 days ago | 0

how to create a vector A [1,1,2,2,3,3] from a vector B [1,2,3]

help repelem

23 days ago | 0

Lsqnonlin problem for calibrating accelerometer

Um, the solution is not to find Q. Because it is difficult to constrain a matrix to be positive definite. You don't want to try ...

23 days ago | 0

control the threshold of random numbers

You just say you want a distribution of numbers that is not uniform. But if you say only what it is not, that is not enough to s...

23 days ago | 0

| accepted

Find the transformation matrix

First, learn to use matrices, NOT numbered variables. Assuming that you have a matrix X, and a matrix Y, with x1 x2, y1, y2 as c...

23 days ago | 1

| accepted

how to solve 3 equations with a known variable and 3 unknown variables

The solution is simple, as I said, and somehow, I imagine you will end up changing the question again. I'll give you an answer, ...

24 days ago | 0

How can I identify the most important independent variable in an equation?

Is it possible? Not really. Not using MATLAB or anything else. You have ONE expression. You might describe the "most important" ...

24 days ago | 0

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Does Matlab have a library for Monte Carlo integration

Do they have a "library"? Not really what I would call a "library". Maybe you might. But why would they? They offer random numbe...

25 days ago | 0

How to get rid of small difference (or error) when I multiply 0.1?

You do understand that MATLAB, as is true of almost any programming language, uses binary storage methods to store all floating ...

30 days ago | 2