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John D'Errico


Retired

Last seen: Today Active since 2006

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.

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Answered
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 ...

ongeveer 17 uur ago | 0

Answered
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...

2 dagen ago | 0

Answered
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...

3 dagen ago | 1

Answered
@ 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...

3 dagen ago | 0

Answered
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...

3 dagen ago | 0

Answered
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...

3 dagen ago | 0

Answered
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...

3 dagen ago | 0

Answered
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 ...

4 dagen ago | 0

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Answered
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...

4 dagen ago | 1

Answered
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...

4 dagen ago | 1

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Answered
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...

5 dagen ago | 0

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Answered
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...

5 dagen ago | 0

Answered
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...

6 dagen ago | 0

Answered
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...

7 dagen ago | 0

Answered
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...

8 dagen ago | 0

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Answered
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 ...

8 dagen ago | 0

| accepted

Answered
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)...

8 dagen ago | 2

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Answered
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...

8 dagen ago | 0

Answered
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...

8 dagen ago | 1

Answered
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? :)

8 dagen ago | 0

| accepted

Answered
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...

10 dagen ago | 1

Answered
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 ...

10 dagen ago | 0

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Answered
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...

11 dagen ago | 0

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Answered
Why are alternative forms for "dbstop in file at location if expression" not documented?
All commands in MATLAB are actually implemented as functions. There is a command/function duality in existence. So you can alway...

11 dagen ago | 0

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Answered
How to adjust a cloud point to meet the minimum distance requirement?
Sorry, but no. There is no analytical solution that would provide the clustering that you wish to achieve. You can use clusterin...

12 dagen ago | 0

Answered
how factor a polynomial into 2 quadratics?
You cannot uniquely factor a 4th degree polynomial into such a pair of quadratics. You may think that you can, but it is provabl...

12 dagen ago | 0

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Answered
seven roots of an equation
Your equation is: What you have done in code is terribly confusing. There is no need to use symsum. Can we assume that b is ...

12 dagen ago | 1

| accepted

Answered
How to get coefficient non linear fit?
% Make up some random data since you gave us none x = rand(50,1); y = 0.3*exp(-2.5*x) + 1 + randn(size(x))/50; plot(x,y,'.') ...

13 dagen ago | 0

Answered
A better way to do antidiagonal matrix vectorization?
This should not be that difficult. One trick might be to use ndgrid, and then a sort. For example, consider the function adunrol...

14 dagen ago | 2

Answered
why in this function they use empty square brackets?
It is not a dumb question at all, because the syntax used by MATLAB to delete a row or column of an array may not be obvious. Bu...

14 dagen ago | 1

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