# 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.

**Statistics**

RANK**10**

of 246.711

REPUTATION**16.456**

CONTRIBUTIONS

**10** Questions

**5.793** Answers

ANSWER ACCEPTANCE **
50.0%
**

VOTES RECEIVED**3.520**

RANK**4** of 17.210

REPUTATION**60.800**

AVERAGE RATING**4.80**

CONTRIBUTIONS**57** Files

DOWNLOADS **1398**

ALL TIME DOWNLOADS**547801**

CONTRIBUTIONS**0 Posts**

CONTRIBUTIONS**0** Public Channels

AVERAGE RATING

CONTRIBUTIONS**0** Highlights

AVERAGE NO. OF LIKES

**Content Feed**

How to format my code in this way? Is there any shortcut?

If you put it in as a picture, then of course not! However, if you paste in the code, then note there is a toolbar on top of th...

alrededor de 2 horas ago | 0

How to match column of a one matrix with another column of second matrix?

A = [ 0 0 3 0 2 3 1 2 0 1 0 0]; B = [ 0 3 0 2 3 0 2 ...

alrededor de 8 horas ago | 0

| accepted

So I tried to write on the screen symsum results, but one of them got a little bit wrong position

syms n fprintf('a) %f\n',symsum((n+3^n)^-1,n,1,2021)) fprintf('b) %f\n',symsum((2*n+1)^n/n^(2*n),n,1,2021)) fprintf('c) %f\n'...

alrededor de 9 horas ago | 0

Is it possible to use the colormap "Purples" in MATLAB, which maps zeros to white?

Um, trivially, yes. (Ok, maybe not trivial. But not difficult.) The biggest question is just to recognize what you want to call ...

alrededor de 13 horas ago | 1

| accepted

Delete the post thanks

The simplest answer is to use my blktridiag utility from the file exchange. full(blktridiag(A,C,B,3)) ans = 1 2 9 ...

alrededor de 13 horas ago | 1

Finding the number of values about nonlinear equations.

You need to understand it is IMPOSSIBLE to know the number of solutions to a general nonlinear equation, or system of them. I...

1 día ago | 0

| accepted

How to integrate between 2 points of a given array.

idx1 idx1 = 2629 idx2 idx2 = 2622 So then what did you do? In order to understand (and then fix) the problem, you need t...

1 día ago | 0

| accepted

Adaptive step size for quasi newton optimization

Sorry, but those tools do not give you direct control of the step size. However, if you are using fminunc, then is there a good ...

2 días ago | 0

| accepted

Calculate this matrix in a more general and shorter way

x is 100x1. Now, suppose we want to generate multiple terms of the form sin(k*w*x), so k will be a vector. w is a fixed constant...

4 días ago | 0

How to solve for N sets of 2 equations and 2 unknowns using a for loop?

If these are LINEAR equations, then using fzolve or vpasolve is actively silly. They are designed to solve much more difficult p...

4 días ago | 1

@ Symbol in function handles as an input variable to another function

Integral will only accept an input function as a function handle. The @ converts the m-file name into a function handle, that in...

4 días ago | 0

How to perform pseudo inverse with set of elements in a matrix?

I think you misunderstand the linear algebra here. A=(1:12).'; B=(1:4).'; A_43 = reshape(A,length(B),[]) % I'll create a vari...

4 días ago | 0

Numerical solution for a complex formula

syms M A y = 1.4; eqn = A == ((1)/(M))*((1+((y-1)/(2))*(M^(2)))/((y+1)/(2)))^((y+1)/(2*(y-1))) Now you wish to solve that exp...

5 días ago | 0

3-dimensional orthonormal rotation symbolical

You have several misunderstandings here. First: phi_x = pi/2; phi_y = 0; phi_z=pi; % Define symbolic variables syms phi_x p...

5 días ago | 0

Plotting multiple inequalities in 3D Space

First, [x,y,x] = meshgrid(-10:0.1:10); Correct code is important in MATLAB. Else it will not know that you really intended ...

5 días ago | 0

| accepted

how can i get value of y

You want to solve for y, as an implicit function of r? First, you should consider if a solution exists at all. Is it multi-valu...

6 días ago | 1

full rank left annihilator matrix

Are you asking to find a MATRIX B that will kill off A when you left multiply B*A? syms x1 x2 x3 x4 Cdc Cb Lcpl Vfc A=[Vfc/(x...

6 días ago | 1

| accepted

How to solve 3 differntial equation by Runge-Kutta 4th order

If you NEED to use Runge-Kutta, then this is a homework assignment, and you are not telling us, because you know that we don't d...

6 días ago | 0

| accepted

Support for older MATLAB versions on new operating systems

Um, lets be rational here. Can The MathWorks control how operating system X changes? They wrote their software to run on X, re...

7 días ago | 0

Trouble using atan2 for coordinate transform, maybe recommend other tools.

The transformation you are using is a simple tranformation into polar coordinates. When you have y in there also, this becomes w...

7 días ago | 0

code for a simple nanogram function

Now roughly a month since the original post, and nobody has answered. I was not sure if this could be a student problem, so I ga...

9 días ago | 0

How can i define a m by n symbolic matrix?

If m and n are themselves symbolic, you cannot do so. However, you can do this: matfun = @(m,n) sym('a',[m,n]); Now you can us...

9 días ago | 0

| accepted

Accuracy of polygon approximation

R*2 is not remotely meaningful here, unless you find a way to intelligently extend it to this situation. I would probably find ...

10 días ago | 0

| accepted

Function value and YDATA sizes are not equal BUT THEY ARE

The expectation is that in the function (here, Cp) the data vector should be the SECOND argument. It needs to be Cp = @(x,T7)...

10 días ago | 2

| accepted

Help Finding Explicit Solution Non Linear Differential Equation

There is no assurance that ever nonlinear differential equatino you may choose to pose has an analytical solution. In fact, I no...

10 días ago | 0

Which is the smallest natural number n to which it applies a(n)>10?

The obvious answer is brute force, thus... a_i = 1; a_iplus1 = 1; plot(a_i,a_iplus1,'o') hold on iter = 2; imax = 1e6; wh...

10 días ago | 1

How to draw a line on a symbolic surface

syms x1 x2 f1 = x1^2+x2^3-9 fsurf(f1); hold on fimplicit(f1,'r') WTP? :)

10 días ago | 0

| accepted

Trying to do product of eigenvalues collected from a matrix

You don't want to use the product of eigenvalues to determine if a matrix is singular. This is equivalent to computing the deter...

12 días ago | 1

Output vector in the polyval

format long g p=[1 0 0 0 0 -5 3 21]; x=[10 15 20]; poly_value=polyval(p,x) poly_value = 9999551 170858316 ...

12 días ago | 0

| accepted

Quadratic/Exponential Best Fit Curve

First, you have 4 data points. Trying to fit a degree 7 (SEVEN) polynomial to that is just silly. Yes, you say quadratic. But yo...

12 días ago | 0

| accepted