# John D'Errico

### Retired

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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**Content Feed**

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...

ongeveer 5 uur ago | 1

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. ...

ongeveer 9 uur ago | 1

| accepted

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...

ongeveer 14 uur ago | 1

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...

1 dag ago | 0

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...

1 dag ago | 1

| accepted

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...

3 dagen ago | 0

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 (...

4 dagen ago | 0

| accepted

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. ...

4 dagen ago | 0

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"; ...

5 dagen ago | 0

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...

5 dagen ago | 1

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 ...

6 dagen ago | 1

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...

6 dagen ago | 1

| accepted

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...

6 dagen ago | 0

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...

7 dagen ago | 0

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...

9 dagen ago | 0

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...

9 dagen ago | 0

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...

11 dagen ago | 0

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 ...

11 dagen ago | 0

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...

12 dagen ago | 0

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...

13 dagen ago | 0

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...

14 dagen ago | 1

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 ...

14 dagen ago | 0

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...

17 dagen ago | 3

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...

17 dagen ago | 1

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...

17 dagen ago | 3

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

19 dagen ago | 0

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...

19 dagen ago | 3

Alternate function of gdivide

help gdivide As you should see, gdivide provides a great deal of very general functionality. And that means it will also includ...

21 dagen ago | 0

| accepted

how create cell 1:10 vertical

There are always many ways to solve a problem. An easy way to create the cell array directly is to do this: C1 = {1;2;3;4;5;6;7...

22 dagen ago | 0

How can I fill the area under a curve with different colors?

Simple. Just use fill (or patch) to fill THREE patches, each with the desired color. How can it be any simpler? Or, you could ...

22 dagen ago | 2