# 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**

Generate a numerical series

While @DGM is correct (+1 from me on that answer, please accept that answer, as it is the correct one), in that it is what I wou...

6 hours ago | 1

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,... ...

1 day 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 ...

4 days ago | 1

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Create a vector from repetition of two others

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

5 days 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 days ago | 1

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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 days 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 days 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...

7 days ago | 1

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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 days ago | 0

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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 days 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 days ago | 0

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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...

9 days 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 ...

9 days ago | 0

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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...

9 days 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 days ago | 2

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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 days ago | 0

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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 days 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...

11 days 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 days ago | 0

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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 days 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 days ago | 0

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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 days ago | 0

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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 days ago | 0

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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...

15 days 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 days 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 days ago | 1

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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 days 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 days 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...

16 days ago | 0

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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 days ago | 0