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John D'Errico


Retired

Last seen: en dag ago |  Active since 2006

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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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Answered
Is there anyway to Re-grid one dataset to another dataset resolution without interpolating??
What you are asking to do is arguably still "interpolation" of a sort. In fact, Walter''s use of nearest neighbor is quite reaso...

en dag ago | 0

Answered
cross multiplication of algebra expression denominators
syms x y a b k eq = y/a == k+x/b Symple enough. :) eq = expand(eq*a*b)

3 dagar ago | 0

| accepted

Answered
Optimal values dynamic programming and mathematical programming
The crystal ball is very foggy today. What does it matter what we think? We know nothing about what you actually did, if the cod...

4 dagar ago | 1

Answered
correlation of nonlinear variables
Correlation does not really make sense in respect to nonlinear variables. Depending on the values of the variables, they will be...

4 dagar ago | 0

Answered
Why does N-D convexhulln give a matrix as an output instead of vector containing indices of inputs?
The convex hull of a 2-d data set will be simply a polygon. So the convex hull code returns the set of points in the polygon, in...

6 dagar ago | 0

| accepted

Answered
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...

11 dagar ago | 0

| accepted

Answered
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...

12 dagar ago | 0

Answered
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...

12 dagar ago | 1

| accepted

Answered
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...

12 dagar ago | 0

Answered
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 ...

12 dagar ago | 1

Answered
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...

16 dagar ago | 0

Answered
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...

17 dagar ago | 0

Answered
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...

18 dagar ago | 0

Answered
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...

19 dagar ago | 0

| accepted

Answered
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 ...

19 dagar ago | 0

Answered
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...

20 dagar ago | 1

Answered
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...

22 dagar ago | 1

| accepted

Answered
FORTRAN POPPAR Equivalent in Matlab
The obvious answer is the simple answer... sum(dec2bin(I) - '0')

26 dagar ago | 0

| accepted

Answered
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...

27 dagar ago | 0

| accepted

Answered
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...

27 dagar ago | 2

| accepted

Answered
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...

27 dagar ago | 1

Answered
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...

28 dagar ago | 0

Answered
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 ...

29 dagar ago | 0

| accepted

Answered
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...

ungefär en månad ago | 0

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Answered
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 ...

ungefär en månad ago | 1

| accepted

Answered
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...

ungefär en månad ago | 0

Answered
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...

ungefär en månad ago | 0

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

ungefär en månad ago | 0

Answered
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 ...

ungefär en månad ago | 0

Answered
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...

ungefär en månad ago | 0

| accepted

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