Community Profile # John D'Errico

### Retired

Last seen: 1 day ago 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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Optimize two variables under two conditions
Um, you cannot optimize TWO things at once. There is no reason to assume that they will both achieve their respective optimal ...

14 hours ago | 0

How to make a data set periodic?
How do you MAKE it periodic? It is either periodic or it is is not. Is the value at 0 the same as that at 2*pi? If not, then wha...

24 hours ago | 0

I want help in writing a matlab code so that I wouldn't have to manually input the various steps as I have shown below. Thanks
R is a matrix. So the statemen while R is meaningless. As well, this if statement if R <= 0.0001; break en...

3 days ago | 0

'manual' t-test gives different result for same t-value
I think you misunderstand what a pdf is, when to use a cdf versus a pdf, or perhaps how the t-test works. Maybe all of those are...

3 days ago | 0

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ode does not appear to give correct answer
I think you misunderstand what is happening. You get a constant in there, in the form of 2*c. But is c an unknown constant? Wou...

3 days ago | 0

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fsolve function random value gives the same output as random value
First, always test how your function operates. That will verify it produces what you expect. theta(ones(5,5)) theta(rand(5,5))...

3 days ago | 0

Matlab wouldn't find simple inverse
There is another possibly more important problem, beyond those mentioned by @Yongjian Feng. While you may, personally think the...

3 days ago | 0

Converting base N to base 10
Why would you special case base 16 anyway? What if they gave you base 15? Or base 19? Or base 12? It is a really bad coding st...

4 days ago | 0

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how can i multiply two complex number in GUI
What is the problem? Convert them to numbers. Multiply said numbers. Then output the result however you desire. My guess is you...

4 days ago | 0

How to remove Outliers
The obvious answer is to look at the tools provided in MATLAB. Thus RMOUTLIERS, ISOUTLIER, etc. They are provided in the stats t...

4 days ago | 0

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...

4 days 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 ...

5 days ago | 0

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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'...

5 days 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 ...

5 days ago | 1

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Create a block diagonal, Toeplitz and triangular matrix given by n,B,C,A
The simplest answer is to use my blktridiag utility from the file exchange. full(blktridiag(A,C,B,3)) ans = 1 2 9 ...

5 days 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...

6 days ago | 0

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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...

6 days ago | 0

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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 ...

7 days ago | 0

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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...

8 days 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...

9 days 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...

9 days 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...

9 days 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...

9 days 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...

9 days 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 ...

10 days ago | 0

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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...

10 days 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...

10 days ago | 1

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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...

11 days ago | 0

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