John D'Errico

Retired

Last seen: Today | Active since 2006

A retired applied mathematician, consultant, sometime mechanical engineer, numerical analyst, woodworker, bridge player. Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. I won't do consulting by mail.

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Answered
How to solve equation with several unknown variables for a specific variable?
When you pose it as you did to solve, solve assumes you are trying to solve TWO equations, one of which is the equation cos...

en dag ago | 1

Answered
How can I plot the innermost contour?
As an aside, since @Cris LaPierre has already suggested the use of LevelList to do the job. And that arguably is the correct ans...

4 dagar ago | 0

| accepted

Answered
why I get the error message like "Attempt to execute SCRIPT bar as a function"?
Don't use existing function names as the names of your own scripts. If you do, then eventually you will get strange errors like ...

6 dagar ago | 0

Answered
Element wise multiplication of a 4D Matrix
A confusing question. MAYBE you are asking how to take the product of the elements along the 4th dimension? That is consistent w...

7 dagar ago | 2

Answered
round() function does not work as expected
Sorry, but it is often the case that your vector X is not what you thought it was, or you have written a function named round. ...

7 dagar ago | 1

| accepted

Answered
How can I cut four numbers after the decimal number without rounding using MATLAB ?
You want to truncate after the 4th decimal place? Easy peasy. You shift where the decimal place lies, then use floor. format l...

7 dagar ago | 2

| accepted

Answered
Why isn't vectorization faster than repeating loop comparing 6 about years ago.
Things change. Vectorization OFTEN is faster. But nothing says it MUST ALWAYS be faster. Remember that vectorization often trade...

8 dagar ago | 1

Answered
Matlab solver for unconstrained convex optimization
Everybody wants things to be incredibly fast. Large problems can take large time. Nothing stops you from writing a simple gradi...

8 dagar ago | 1

| accepted

Answered
Non-square matrix inverse
You CANNOT do so. That is, you cannot learn the original values. You cannot go backwards. A simple example is: Choose any two n...

9 dagar ago | 0

Answered
How do i make an exponential curve graph from a vector?
You can't have a polynomial that will fit that curve shape. They simply do not have that characteristic form. So using polyfit (...

10 dagar ago | 0

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Answered
How do I get normal numerical answers using solve or vpasolve?
vpa will turn those products involving pi into more normal looking numbers. For example... x = 17*sym(pi) So x has pi in it. ...

10 dagar ago | 0

Answered
Why these two path strings are different? (manual string vs. pwd + fullfile)
LOOK AT THE STRINGS. They are just strings after all. What is different between them? pwd = "C:\Users\username\certain_path"; ...

11 dagar ago | 0

Answered
symbolic solving system of non-linear equations
Solve does not apply to over-determined problems. But it does not know there may be some exact solution that solves the entire s...

11 dagar ago | 1

Answered
Optimization problem using fminunc
Apparently, your objective function is not well defined at the initial point. I know, this is a wild guess, but that is exactly ...

12 dagar ago | 1

Answered
Interpolation of inaccurate datapoints
Interpolation does NOT allow the data to change. Essentially, that is what interpolation means. You need to do SMOOTHING, not in...

12 dagar ago | 1

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Answered
Change variable name across code lines
Use find and replace. It will search for the next occurence of a. Then you click on either replace, or to ignore that occurenc...

12 dagar ago | 0

Answered
How can I find the determinant and transpose of a 13*13 matrix without writing all the numbers one by one?
You have many almost random looking numbers. So without knowing how they were generate, it is impossible to do better than stuff...

14 dagar ago | 0

Answered
i'd like to ask is there any function to find asymptotes of an equation y = f(x) that satisfies x = x(t) and y = y(t). I'm new to matlab.
Its an interesting question of mathematics, maybe not really a question about MATLAB in my eyes, because until you know how to s...

15 dagar ago | 0

Answered
how to suggest a name to save
Asking a computer to suggest a name is impossible. It cannot know what name might be appropriate, and more importantly, what you...

15 dagar ago | 0

Answered
solve function answer is a 2x1 matrix . how to assign it directly to 2 variables ?
For example, I'll compute the mean of an array, which here will generate a vector of length 2. A = rand(10,2); mean(A,1) Defi...

17 dagar ago | 0

Answered
How to use substitution on function handle?
ODE45 CANNOT use symbolic parameters. PERIOD. No matter how you try to trick things, you cannot pass a symbolic parameter (here ...

17 dagar ago | 0

Answered
Coefficents of piecewise polynomial in matlab
Do you understand the result will not be some simple polynomial like you are used to seeing? plot([1 0 -1 0 1],[0 1 0 -1 0...

18 dagar ago | 0

Answered
need source code for voronoi
Sorry. MathWorks does not give out source code for compiled functions. So unless you are employed there, you don't get the sourc...

20 dagar ago | 0

Answered
Find zeropoints with interpolation
Almost trivial. LEARN TO USE MATLAB! I'll start with a long vector. x = linspace(0,20,1e7)'; y = cos(x); Yes, we know where t...

20 dagar ago | 1

Answered
I need help with cubic splines containing pre existing conditions
Easy enough. And ... also somewhat useless, because this is not how you will have been asked to solve the problem. But it might ...

21 dagar ago | 0

Answered
I have a problem with the convergence of fsolve ?
Solve simpler problems. Choose even better starting values. Yes, you think yours are reasonable, but they are not as good as yo...

23 dagar ago | 3

Answered
Indexing with min and numel
vector1 = 1:5 vector2 = 2:7 N = max(numel(vector1), numel(vector2)) I'm not sure what you mean by indexing. But the above see...

23 dagar ago | 1

Answered
Dsolve gives extra term
Why do you care? Note that C1 is completely arbirtrary! C1 is an unknown constant! So you can trivially add or subtract any c...

24 dagar ago | 3

Answered
How to find the best combinations of calculation of function with 36 input constants, each constant is possible to calculate in 3 ways
Brute force is NEVER going to be a good idea. Instead, if you have the global optimization toolbox... help ga

25 dagar ago | 0

Answered
which method is usied to solve the Determinant in Matlab
JUST READ THE HELP! (Actually, doc det.) In there, you will see this statement: det computes the determinant from the triangula...

26 dagar ago | 3