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John D'Errico


Retired

Last seen: Today Active since 2006

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
Random number generation with min, max and mean
Sigh. I've probably seen different variations of this question asked at least many hundreds of times over the 40+ years I have b...

environ 21 heures ago | 0

Answered
fit tool with errors in x and y
You can't. Period. You cannot use fit to solve a problem with errors in both x and y. That does not say the problam is never sol...

environ 21 heures ago | 0

Answered
roots(x) vs root= interp1(y,x,0)
You need to understand the mathematics. Lost you will be without that (to misquote someone named Yoda.) For this polynomial: s...

2 jours ago | 0

Answered
How to create random matrix with specified step in interval [a, b]
You can also use indexing. The idea is to generate random indexes. ValidRandomSet = 5:3:34 m = 7; n = 6; ind = randi(numel(V...

3 jours ago | 2

Answered
Interpolate using a different method without the original image
Um, no, or, yes. Anyway, you cannot do it directly. And it may be completely impossible to do. All of that depends on several th...

6 jours ago | 0

Answered
How to find the volume of cross-sectional area of a cylinder
Is there a ready made function that will do the mathematics for you, based only on an inequality? No. You will need to do some m...

6 jours ago | 0

| accepted

Answered
Error solving bvp4c - Singular jacobian
You have a simple classical ODE, with two INITIAL conditions, not boundary conditions at different ends. So use a tool like ODE4...

8 jours ago | 0

Answered
noisy plot after calculating first derivative
You should recognize that differentiation is a noise amplification operator. So any small amounts of noise in your signal, even ...

9 jours ago | 0

| accepted

Answered
fminsearch with side conditions
Generally, the solution is to not use fminsearch. Use a better optimizer instead. It will be faster, and you will get a better a...

9 jours ago | 0

Answered
Obtaining value of highest order derivative over simulation period
Can you use schemes like ODE45, combined with gradient to compute exact estimates of the high order derivatives? Sadly, no. High...

9 jours ago | 1

Answered
Acceleration at the center of the triangle
If you have some known parameter at the three corners of a triangle, then the best estimator of that parameter at the center of ...

10 jours ago | 1

Answered
How to use bitn
You cannot define a scalar variable as a binary one with an arbitrary number of bits. You can define integer variables, with a s...

11 jours ago | 0

Answered
Why I'm getting error (too many arguments) in my integral
You need to pay MUCH more attention to your code. For example, just a quick look shows this: Intdoble6=int(int(2*y^2,x,0,1)4*x...

12 jours ago | 0

Answered
I nee to write a code to solve a definite integral. The output format has to be fprintf.
Do you understand that MATLAB REQUIRES a multiplication operator? You cannot just put a number next to a letter, and expect MATL...

12 jours ago | 1

Answered
Maximum Likelihood Estimation function
Is there another way? Why not negate the function, and then use a tool like fminbnd? Or fminsearch. Or fmincon or fminunc, or .....

14 jours ago | 0

Answered
What optimizer should I use?
This is not a problem of finding an optimizer. This is a problem of understanding how to formulate a problem so that it is possi...

14 jours ago | 0

Answered
simulation stopped because of step size tolerance and constraints
Let me see. You posed an optimization problem. The solver returned a result, one that SATISFIES the tolerances you posed. You we...

14 jours ago | 0

Answered
Revolving a curve about the y-axis to generate a 3D surface
Certainly. Just write the code yourself. Seriously, it is not difficult. Consider the function y = f(x). f = @(x) x.*(1-x); ...

15 jours ago | 0

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Answered
matlab rank of a matrix
Because the call: R = ones(100,100); rank(R,1e-20) attempts to do something that is demonstrably silly, in terms of double pr...

15 jours ago | 0

| accepted

Answered
which project of these projects will be easy with matlab?
I think you do not understand. ANY project can be either easy, or too difficult for you to handle. What matters is if you unders...

19 jours ago | 0

Answered
How should I approach solving differential equation as function of two variables r, k?
While you COULD use an ODE solver, this is something you would ONLY do if the ODE had no analytical solution. And this ODE has a...

20 jours ago | 1

Answered
Fmincon too many input arguments
How are you using it? That is, how did you call the function try_no_gradient(u0)? When you get an error message, show the COMPL...

20 jours ago | 0

Answered
How to subtract only certain elements of a vector
a and b are not vectors in your question, they are arrays. However, if you want to do this, nothing stops you from selecting th...

21 jours ago | 0

| accepted

Answered
Plot the graph using non linear equation
A nonlinear problem like this is called an implicit function. You can think of the value of h, as a function of theta, but there...

21 jours ago | 1

Answered
convert current date and time to char
Easier than you think. First, what is the current time? format long g CurrentTime = now That might not seem terribly helpfu...

22 jours ago | 1

Answered
Limit angle in [-90,90] degree
You cannot simply constrain an ODE solver to stay within bounds. However, almost certainly, if the ODE solver wants to go outsid...

24 jours ago | 0

Answered
Code involving factorials and a given value
Now that you have a looped solution, let me show how to solve the problem more directly. There are actually several solutions I ...

25 jours ago | 1

Answered
how to solve this differential equation system symbolically?
This seems like a homework problem. But Walter has already given an answer, that I think is not helpful, since dsolve will fail ...

25 jours ago | 0

| accepted

Answered
Optimization to find a deterministic number
Huh? This question is pretty confusing. But let me see where it goes. First, it seems you claim that g(x) is the solution of an...

26 jours ago | 0

Answered
How to rotate about an axis parallel to x axis?
Simple. Effectively, you transform the problem to a rotation around the x axis, then after the rotation, you tranform back. For...

27 jours ago | 1

| accepted

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