John D'Errico
Last seen: Today
Retired
5 716 total contributions since 2006DON'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.
John D'Errico's Badges
Answer 50 questions that were unanswered for more than 30 days
Awarded to John D'Errico on 15 Nov 2020
Contribute at least one answer each month for 36 consecutive months
Awarded to John D'Errico on 20 Jul 2017
Obtain 50 solvers for a problem you have created
Awarded to John D'Errico on 10 Sep 2020
Like a problem or solution
Awarded to John D'Errico on 13 Oct 2016
Be the first to solve a problem
Awarded to John D'Errico on 28 Aug 2016
Top ten contributors with the most downloaded submissions
Awarded to John D'Errico on 04 Jan 2021
Top ten contributors with the most downloaded submissions
Awarded to John D'Errico on 02 Jan 2020
Your submissions were downloaded 1000 or more times in a month
Awarded to John D'Errico on 01 Nov 2019
Your submission is selected as "Pick of The Week"
Awarded to John D'Errico on 09 Oct 2019
Publish your first comment or rating
Awarded to John D'Errico on 09 Oct 2019
Your submissions received 25 five star ratings
Awarded to John D'Errico on 09 Oct 2019
Publish your first submission
Awarded to John D'Errico on 09 Oct 2019
Accept 50 answers given by other contributors
Awarded to John D'Errico on 20 Jul 2017
100 of your answers have been accepted
Awarded to John D'Errico on 20 Jul 2017
3D best fit curve from x,y and z data points
You may think it is easy, if only you can find someone who has the magic touch. Sorry, but not so easy. If the curve is presum...
ungefär 13 timmar ago | 0
HOW TO GET THE VALUES OF CONSTANTS
Please don't YELL! Next, NEVER define pi. pi already exists, and I hate to tell you, it ain't 3.14. That only happens in certai...
ungefär 18 timmar ago | 0
Code help on Euler's method
What you need to understand is that Euler is a poor method to use. Easy to write, easy to understand. But is it good? NO. And th...
3 dagar ago | 1
Can I change a 3-tensor into a matrix by indexing with a matrix?
A = randn(4,4,3) % Not very creative in making up numbers. So sue me. :) [~,I] = min(abs(A),[],3) What is I? For every combina...
3 dagar ago | 1
| accepted
Newton Raphson Method not solving
This answer is here just to add some information. I try to teach that one should always plot everything, then look at what they ...
4 dagar ago | 0
How do I fit along the curve.
Why would there be code written to do something completely strange? Well, perhaps I should not call it strange, but your idea of...
4 dagar ago | 0
Interpolation error for one column increasing and one column decreasing
This is impossible to answer, since what you show is clearly not what you have. The error that is given indicates the vector (x...
4 dagar ago | 1
How can I test a long function in Matlab?
Don't test your long function. Because you should be writing SHORT functions. Then you can test each piece, verify it works as d...
5 dagar ago | 0
Simple limit returning NaN: f(x) = exp(-1/x)
Think of it like this. For a limit to exist at x==0, it MUST have the same limit as x approaches 0 from above, as it does when x...
5 dagar ago | 1
| accepted
Continuity of a function in a interval
It may seem basic to you. However, that just means you need to understand computing and floating point arithmetic. Nope. In fac...
5 dagar ago | 0
How to stop MATLAB from opening every time I switch on my computer?
This is not MATLAB that is your problem, but your MAC, and what you apparently told it to do. :) You have MATLAB set as a start...
6 dagar ago | 0
understanding "<" operator line
In order to understand this, I'd STRONGLY recommend you do the MATLAB Onramp tutorials. Try some examples. Look at what happens!...
7 dagar ago | 0
| accepted
Logical indexing of table failing
No. You do NOT know it contains 0.35. In fact, MATLAB cannot represent 0.35 exactly in floating point arithmetic. This is for th...
7 dagar ago | 0
Summing using simspons rule for a given range
If I might suggest, your goal is actively a poor one. Why? Simpson's rule is a higher order rule. It tries to give you a higher...
8 dagar ago | 0
Successive over-relaxation of Laplace equation is converging to slightly wrong value. Floating-point error or code error?
To understand what is happening, you need to first understand what the equations represent! Is this effectively a partial diffe...
8 dagar ago | 0
How can I find the eigenvalues of an n-by-n matrix using For Loops?
Simpler than what Matt has suggested is to just use matrix multiplication, coupled with deflation. That is, can you find the LA...
8 dagar ago | 0
Linear approximation of data set's points.
Don't do it that way!!!!!!! You cannot achieve a continuous piecewise linear function that way. Instead, use a tool designed to ...
8 dagar ago | 1
Matlab integration of numerical data
In order for it to be truly general, you will need to interpolate the "function". For example, we might do this: x = 0:10; y =...
9 dagar ago | 0
How to select complementary elements from a vector?
d = [3 2 1 5 6 7 8 9 0]; I = [1 3 7]; setdiff(d,I) Note that your example is actually incorrect, in that you claim 7 should...
10 dagar ago | 0
Applying Newton's Method to Sound Level Equation
Since we cannot solve it directly.... Are you absolutely positive of that? L0 = 80; beta = 32.2; L = 20; syms r solve(L0...
10 dagar ago | 0
Output all possible results on a 7 equation system
First, it can be proven that not all mathematical equations of this sort can be "solved". This goes back as far as Abel-Ruffini....
10 dagar ago | 1
| accepted
solving equations with trigonometric functions
Note that x1, x2, x5, x6 are just NUMBERS. Defining them as syms in advance does nothing. MATLAB is a language with dynamic vari...
11 dagar ago | 1
error in matrix multiplication while solving system of differential equations
What you do not understand is that the exponential function is exp. Thus, instead of writing e^(-t), you write exp(-t). Next, y...
11 dagar ago | 0
How to solve an optimization problem over two variables using fmincon?
You CANNOT use fmincon on a problem with binary variables or any form of discrete variables. However, IF y is indeed binary, th...
12 dagar ago | 0
Equation to Matlab code
ALWAYS show what you wrote. Ony you know what you mean by dealing with vectors, etc. In the first case, do you have a vector of ...
12 dagar ago | 0
| accepted
How to calculate partial area-under-the-curve?
After all of those comments, to be honest, sorry, but you were both working far too hard on a moderately simple problem. Simpl...
13 dagar ago | 0
How to call fminsearch on my function
Um, you misunderstand the problem. Your function has TWO arguments. PR and PC, both of which you want to be optimized. And while...
13 dagar ago | 0
Uniform Random Variable PDF
What are you doing wrong? Um, pretty much everything? Sorry, but true. ;) However, you do seem to have made some credible effort...
14 dagar ago | 0
Solving Exponencial fuction is not returning the right answer
Yes, you THINK the true answer is 3. But it is not. format long g log(2653/2500) / log(51/50) And that is effectively the exa...
15 dagar ago | 1
| accepted
Solving an inequation of first degree issue
syms x a = 3*x + 21 <= 5*x + 13 asol = solve(a,'returnconditions',true) asol.x asol.conditions It looks like x >= 4 is the ...
15 dagar ago | 1
| accepted
Select a Web Site
Choose a web site to get translated content where available and see local events and offers. Based on your location, we recommend that you select: .
Select web siteYou can also select a web site from the following list:
Americas
- América Latina (Español)
- Canada (English)
- United States (English)
Europe
- Belgium (English)
- Denmark (English)
- Deutschland (Deutsch)
- España (Español)
- Finland (English)
- France (Français)
- Ireland (English)
- Italia (Italiano)
- Luxembourg (English)
- Netherlands (English)
- Norway (English)
- Österreich (Deutsch)
- Portugal (English)
- Sweden (English)
- Switzerland
- United Kingdom (English)