# 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**

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

| accepted

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

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

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

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

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

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

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

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

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

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

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

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