# John D'Errico

### Retired

Please DON'T contact me, as too many students then decide I am their personal consultant if I allow it. Anyway. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting by mail. A retired mathematician, numerical analyst, woodworker, bridge player.

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**Content Feed**

Philosophical question: How to get a vector from the output of solve? Why isn't it a vector already?

I tried it with a vector, wondering if that might make solve work more easily. And it does work. A = magic(3); X = sym('X',[3,...

ungefär en timme ago | 0

Why does fmincon using the sqp algorithm need a full matrix to specify linear constraints?

This sounds like a good excuse for a feature request to me. However, my gut tells me there is a technical reason in the algorith...

ungefär 4 timmar ago | 0

How to build a function fun that takes as input the matrix A and as output provides the matrix B which is produced out of A in the following ways.

Possibly homework. (I never trust simple problems like this, where the goal is simply to move thigns around in a matrix. They ar...

ungefär 6 timmar ago | 0

How to get numerical values of nonlinear implicit function?

This is far easier then you may think. Um, trivially so. Just solve for t, as a function of y. Pencil and paper suffice for that...

ungefär 20 timmar ago | 0

How to write the equation in matlab I= A A* T² exp (qob/kT) exp (q(V - Rs I /kT)) (exp (-1/n) ? Why is the curve not shown in the drawing?

n=5.2; %Ideality factor A =8.16; %Richardson constant q = 1.602e-19; % electron charge K = 1.380e-23; %Boltzmann constant...

ungefär 23 timmar ago | 0

How to find a point on this plot?

X = [-205078000000000.00 -190430000000000.00 -175781000000000.00 -156250000000000.00 -141602000000000.00 -117188000000000.0...

ungefär 23 timmar ago | 0

| accepted

How to find a coordinate of a circle with a given equation tangent to the circle

You (apparently) want to find the circle of radius 4, with center at (0,y0), where y0 is unknown, that is tangent to the curve. ...

en dag ago | 0

Fsolve can't solve this simple nonlinear equation

c = 3; eq = @(z) c - (z.^3/3 - z); [xsol,fval,exitflag] = fsolve(eq,0) fplot(eq,'b') hold on plot(xsol,fval,'rs') grid o...

en dag ago | 2

Unrecognized function or variable 'imnoise2'.

which imnoise2 -all We cannot help you to use a function that does not exist as part of MATLAB, Possibly, the code you are usi...

en dag ago | 0

how to construct this in matlab? can anyone explain step by step?

One line of code. The explanation is right there. If you want more depth, the read the doc for jacobian. The good thing is, MATL...

en dag ago | 0

Colon syntax for creating a sequence of numbers that skips a given number?

You can't, at least not directly. But it is quite simple. For example: setdiff(1:10,3) % 1:10, missing 3 There are probably ot...

2 dagar ago | 0

normalizing a normal distribution

You don't show the actual mean and standard deviation used for that plot, so I'll make a wild guess. mu = 0.55; S = 0.18; fpl...

2 dagar ago | 0

How can I calculate the index of when the sequence starts to repeat?

Why is it clear? It is not certain that it repeats at the points you have indicated. For example, what is the repeating sequenc...

2 dagar ago | 0

Caesar's cypher working incorrectly

Question: What do the functions upper, and islower do in MATLAB? help upper So upper converts a string to entirely uppercase. ...

2 dagar ago | 0

2nd Order ODE Euler method not producing expected results

That is not uncommon with Euler. It can be an unstable method. At each step, a small amount of error gets added in. Eventually,...

3 dagar ago | 0

Is possible to integrate numerical data using quadrature method?

TRAPZ already is a quadrature method!!!!! TRAPZ is an implementation of trapezoidal integration, i.e., QUADRATURE. Where do you...

3 dagar ago | 0

factorization of Multivariate polynomial

This is a bit of a hack of course, since factor seemingly should have solved the problem with the appropriate setting. The probl...

3 dagar ago | 0

I'd like to skip the file that's not there and bring it up!

mat rap? Is that some godawful new song I've never heard before? ;-) That just seems, well, raprehensible to me. You don't want...

3 dagar ago | 0

| accepted

Most efficient way of looking up values in an array.

It hurts my head to see this ordering: (y1, x2, y2 and x1). Sigh. Why? Whatever floats your boat, I guess. I would not be usin...

3 dagar ago | 0

| accepted

matlab some polyfit problem

It is NOT abnormal. It is perfectly normal, and, in fact, perfectly correct. And the scaling is actually a valuable tool, when n...

3 dagar ago | 0

how to use big prime in meshgrid

Pick some random integer X, less than p. You will need to use some tool capable of working with large integers, greater than the...

4 dagar ago | 1

| accepted

Find column number for every row in matrix

Simple. One line. A = randi([-5,5],[10,7]) [~,col] = max(A > 0,[],2) Why does it work? A > 0 returns an array that is true (1...

5 dagar ago | 0

Does the eig() function return normalize eigen vector (unit length)?

Yes. V is normalized to have unit 2-norm, at least in common cases. Surely you could have checked that? A = magic(5); [V,D] = ...

6 dagar ago | 0

| accepted

Solving differential equation in series general solution

I just showed you how to solve the problem, for two unknown constants. Of course, your question here involves an initial value a...

6 dagar ago | 0

How to solve differential equation of series general solution

Assuming I typed in that line correctly... syms y(x) S = dsolve(8*x^2*diff(y,2)+10*x*diff(y)+(x-1)*y==0,'ExpansionPoint',0, 'O...

6 dagar ago | 1

Inquiry about Neural Network Structure for Lane Keeping Assist Example

Answers is not the MATLAB support team. Answers is purely volunteer supported. We have no acess to the information you would wan...

6 dagar ago | 0

Simple loop with equation problem

Looking at your code... Learn to use semi-colons at the end of your lines. This avoids crap being dumped into the command windo...

7 dagar ago | 0

How to plot ellipse using contour function?

I'm a little confused. You DID draw ellipses. It seems the goal was not to draw the ellipses you drew though. Essentially, as yo...

7 dagar ago | 0

Problems accepting integer values with power and algebraic symbols using inputdlg

You could just learn to use the standard scientific notation. So 123e4, which represents 123*10^4. 123e4 Or, you could see tha...

7 dagar ago | 0

| accepted