# 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.

**Statistics**

RANK**10**

of 250.395

REPUTATION**16.868**

CONTRIBUTIONS

**10** Questions

**5.922** Answers

ANSWER ACCEPTANCE **
50.0%
**

VOTES RECEIVED**3.607**

RANK**4** of 17.398

REPUTATION**61.122**

AVERAGE RATING**4.80**

CONTRIBUTIONS**57** Files

DOWNLOADS **1235**

ALL TIME DOWNLOADS**550338**

CONTRIBUTIONS**0 Posts**

CONTRIBUTIONS**0** Public Channels

AVERAGE RATING

CONTRIBUTIONS**0** Highlights

AVERAGE NO. OF LIKES

**Content Feed**

Solve a System of five non linear equation

E_i=[( w1*gamma(mu1+1/a1)/( ( mu1^(1/a1) )*gamma(mu1) ) )+( (1-w1)*gamma(mu2+1/a2)/( ( mu2^(1/a2) )*gamma(mu2) ) )==C1,... ...

alrededor de 18 horas ago | 0

Which is Better for Polynomial Equations: roots or solve?

Roots versus solve can be VERY different in the result. The answer is you need to understand the differences. When is increased ...

3 días ago | 1

| accepted

Create a vector from repetition of two others

A=[1 2 3 4 5]; B=[6 7 8 9 10]; reshape([A;B],1,[])

4 días ago | 1

issue with 'intersect' function

I'm sorry, but your problem lies in understanding floating point arithmetic. Two sets of floating point numbers, created by even...

5 días ago | 1

| accepted

common tangent of double-well function

This is actually not a difficult problem to solve, IF you think about what a tangent line means. For example, consider the pol...

6 días ago | 1

I want to find rate constant from function fminsearch.

Here is a start. First, fminsearch will probably be a poor solver to use here. At least, make sure you have good starting values...

6 días ago | 0

How can I solve this problem in MATLAB? Warning!

That you need to solve it is not relevant. Does an analytical solution exist? Almost surely not. We all sometimes want for thing...

6 días ago | 1

| accepted

Finding all local/global minima of an Optimization Problem

Do you understand there are infinitely many such equivalent solutions to that problem, not just TWO? And, while I'd like to writ...

8 días ago | 0

| accepted

how to make a vector z that consists of odd-indexed entries of y (y=[100:1])?

A very confusing question. I'll take a wild guess. If this does not answer your question, then you need to be FAR more lear. y ...

8 días ago | 0

Is applying a binary operator (+,-,*,/) to char arrays supported by MATLAB or just a "trick"

The plus operator has long been supported, as it applies to character arrays. I recall it existing for as long as I go back usin...

8 días ago | 0

| accepted

if statement for every possibility

Ok. Let me see if I understand. A wierd number x is a positive integer, such that given the set of proper divisors of x (that is...

8 días ago | 2

random matrix with a minimum number difference for adjacent numbers accepted

Let me start out by saying it is a terrible idea to use max and min as variable names. Your next anguished question will be why ...

8 días ago | 0

| accepted

How to solve for unknown function in integral equation?

One idea can lie in the use of a family of functions the decompose the unknown f. Choose an orthogonal family over the chosen do...

8 días ago | 0

Numeric derivative with multiple variables

Here is a simple trick to remember. See how I used da1 and da2 below. f = @(a) sin(a(1)) + cos(a(2)) + a(1) - 2*a(2); a0 = [...

9 días ago | 2

| accepted

Is there any easy way to calculate integral with cylinder coordinates in Matlab numerically?

It seems pretty easy. Go back to calc 101. Maybe 102. WTP? For example, what is the integral of z*(x^2+y^2), over a unit cylind...

9 días ago | 0

| accepted

How to get multi-solution using 'lsqnonlin'?

lsqnonlin is a numerical optimization tool. It iterations fro mthe start point to a solution. And the solution you get is depend...

9 días ago | 1

What can I use instead of 'lsqcurvefit'

A solver CANNOT know if it is in the global minimum or a local minimum. Even a putatively "global" solver cannot be certain exce...

10 días ago | 0

What is the meaning of sol(31,: ,1)

Do you understand indexing? Perhaps you really need to start with a tutorial, the Onramp tutorials may be a good place to start....

12 días ago | 0

| accepted

How to show an answer in decimal

a = 0.25; b = 0.5; T = 0.07; k1 = 0.6; k2 = 0.55; k3 = 1; sympref('FloatingPointOutput',true) syms s ; expr =(T.*s+k2)....

14 días ago | 0

A very strange problem

I suppose this is a subtle problem that bears explanation. D0=1;D1=1; f='@(dt)[(-D0)*dt^0.5+(-D0*D1)*dt^1.5/2;1/2*(-1+(1)+(2*D...

14 días ago | 0

| accepted

MatLab single precision epsilon versus double precision epsilon

By the way. I am 100% sure that MATLAB's machine epsilon is correct for both single and double. :) One subtle issue lies in the...

14 días ago | 0

| accepted

A matlab function is not running. Can someone help me?

No problem. It runs fine, using EXACTLY the code you posted. I will point out that when you report an error, please report the ...

14 días ago | 0

| accepted

Time arithmetic (no dates)

4:30 is not a number. In order for you to work with something like that, you need to first convert it to a vector of TWO numbers...

14 días ago | 0

Is it possible to create a modular equation solver?

Is it possible? Um. sure. Virtually anything is possible. But having lots of things in separate m-files is a bad idea here. Now ...

15 días ago | 0

Excluding 0.5 from rounding

You cannot do this. That is, there are only a few specific classes of rounds you can do, embodied in round, fix, floor, and ceil...

15 días ago | 1

| accepted

Where is the library ?

There are two hits I found for quaternion.m. One is one the file exchange, where you can download it. https://www.mathworks.com...

15 días ago | 0

I am trying to find values of four constants from four equations. Yet the code is unable to give out values

When will people learn to use vectors instead of numbering their variables? And learn to use semicolons on your lines, in the ri...

15 días ago | 0

How to fit an uniform distribution to a histogram?

If you have histfit, then you would also have unifit. data = unifrnd(-100,100,1000,1); [AHAT,BHAT,ACI,BCI] = unifit(data) his...

15 días ago | 0

| accepted

The lowest distance of two points on two curves

PDIST, from the stats toolbox can compute the set of all interpoint distances between two sets of data. Then you could just take...

16 días ago | 0

how to use betafit for a data that is outside the range of 0 to 1.?

You essentially have a 4 parameter beta distribution that you wish to fit. That is, the upper and lower limits can be part of it...

16 días ago | 0

| accepted