# 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**

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...

ungefär 3 timmar 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 ...

ungefär 19 timmar 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...

ungefär 19 timmar 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...

en dag 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 ...

2 dagar 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...

4 dagar 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...

4 dagar 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...

5 dagar 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 .....

6 dagar 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...

6 dagar 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...

7 dagar 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); ...

7 dagar 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...

7 dagar 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...

11 dagar 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...

12 dagar 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...

13 dagar 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...

13 dagar 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...

13 dagar 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...

14 dagar 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...

16 dagar 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 ...

17 dagar 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 ...

17 dagar 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...

18 dagar 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...

20 dagar 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...

20 dagar 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...

21 dagar ago | 0

| accepted

Calculate the distance between points in a large data set

LEARN TO USE MATLAB. Do not create numbered and named variables. DO create vectors and arrays. Use them. Since all you have pos...

22 dagar ago | 1

| accepted

Optimization terminated: average change in the fitness value less than options.FunctionTolerance.

Star has answered your uestion. However, I want to expand on what was said there. Too often, I see people confused by this messa...

23 dagar ago | 0

Describe non-convex region with linear inequality constraints

Nothing stops you from dissecting a polygonal region into triangles, even if not convex. As Matt said, you CANNOT use a set of l...

23 dagar ago | 0

How to find area of enclosed region (i.e., calculate Green's Theorem) in MATLAB?

You have a sequence of points in a loop. Create a potyshape from them, then compute the area. help polyshape methods polyshape...

24 dagar ago | 0