# 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**

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...

etwa 5 Stunden 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...

2 Tage 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...

4 Tage 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...

4 Tage 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...

6 Tage 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 ...

7 Tage 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...

7 Tage 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...

7 Tage 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 ...

8 Tage 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...

10 Tage 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...

10 Tage 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...

11 Tage 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 .....

12 Tage 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...

13 Tage 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...

13 Tage 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); ...

13 Tage 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...

13 Tage 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...

18 Tage 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...

18 Tage 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...

19 Tage 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...

19 Tage 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...

19 Tage 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...

20 Tage 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...

22 Tage 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 ...

23 Tage 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 ...

23 Tage 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...

24 Tage 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...

26 Tage ago | 1

| accepted

Matrix from measured data is singular, what could be the reason?

In no place in this thread have I seen the matrix A. I've seen various versions of it however, with various numbers of rows. I'v...

26 Tage ago | 0

Reinforcement Learning toolbox missing functions

If you have a current version of that toolbox, it should have those tools. which rlDiscreteCategoricalActor which rlValueFunct...

27 Tage ago | 0

| accepted