John D'Errico

Retired

Last seen: Today | Aktiv seit 2006

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. Anyway. I won't answer questions. PERIOD. I don't do your homework. I won't do consulting by mail.

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3D Surface of revolution from a 2D perimeter
Ok. (I should probably write code to do this in general, for any arbitrary polygon.) Quad elements. I'll show how to do it for ...

etwa 17 Stunden vor | 0

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Solving a set of 8 non-linear equations using symbolic toolbox results in empty sym 0 by 1
NO. The equation POSSIBLY has a solution. In theory, it MIGHT have a solution. But having a theoretical solution does not mean i...

etwa 20 Stunden vor | 0

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Find Indefinite Integral from Array Values
Sorry. there is no need for them to be exactly the same. Cumtrapz is a simple variation of a fixed stepsize Euler integration,...

ein Tag vor | 1

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How can I find a multiplication coefficient between two signal?
Your need is to solve the problem signal2 = constant*signal1 Where the variable "constant" is unknown. This is easy to solv...

ein Tag vor | 0

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Equation solution is not found for all array element
For SOME of these sub-problems, no solution was found. I would suggest that when the result from vpasolve is empty, you could ...

ein Tag vor | 0

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How to reduce dimensionality of a rectangular matrix
Your matrix has size 640000 by 288. So there are only 288 pieces of distinct information in your data. You CANNOT use PCA to do ...

ein Tag vor | 0

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Symbolic acos( cos(theta) ) does not return theta.
Is it true, that acos(cos(theta)) ALWAYS returns theta? TRY AN EXAMPLE. acos(cos(10)) So it is not true. It works the other wa...

ein Tag vor | 0

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curve fitting of two equation to two data sets simultaneously
Are the values of x the same for the two vectors y1 and y2? You don't show any data, so it is difficult to help more, as there ...

2 Tage vor | 0

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Create a single variable to store multiple correlation coefficients
A = rand(300,7); B = rand(1,300); C = corrcoef([A,B']); C = C(8,1:7) The correlation coefficiens of each column of A, agai...

2 Tage vor | 1

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How do I remove every row that has a zero in it?
TSLA = rand(366,7); TSLA(TSLA(:,4) == 0,:) = []; One line. No loops.

3 Tage vor | 0

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Creating a mxn matrix that is all zeros except for the middle row and middle column which are 1s
Clearly a homework assignment. But now long since past, and with multiple answers, most of which are not in one line. However, s...

3 Tage vor | 0

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find the index number using bsxfun command
But why would you use bsxfun at all to do this? A = [12 13 15 1]; B = [1 2 12 15 10 13 11 14 3 4 5 6 7 8 9 16]; Use ismember ...

3 Tage vor | 0

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How can I rearrange equations to general form?
syms x y z eqn1=x+y+5==-z Nothing stops you from doing it yourself. For example, I might do: eqn1 = eqn1 + z Or, you can ev...

3 Tage vor | 0

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Inverse computation with a starting guess
It is often the case that someone THINKs they need a matrix inverse, yet they don't. And since you don't know if you can do this...

5 Tage vor | 0

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Vectorization approach to find matching elements in a matrix.
The part of your code that is a serious problem is where you build the arrays by growing them at each step. This is a really bad...

5 Tage vor | 0

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Please how can I calculate the values of this finite sum of numbers in fully sequential , I'm finding it difficult
Easy peasy. sumof4thpowers = @(N) nchoosek(N+1,5) + 11*nchoosek(N+2,5) + 11*nchoosek(N+3,5) + nchoosek(N+4,5); For example: s...

5 Tage vor | 0

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optimization in smart energy management system.I have used MILP algorithm but i got infeasible solution no point satisfy the constraints.how could i sort out these issues.
No solution means exactly what it sounds like. NO solution. And for this class of problem, if it tells you that NO solution exis...

5 Tage vor | 1

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How to find derivatives using the diff command
There are two versions of diff in MATLAB. One operates on numeric vectors and arrays. It simply subtracts each number from the o...

6 Tage vor | 0

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Sum two matrices shifted by a non integer number?
There is no magic, whereby you can do things that take computational time, and do them instantly. What you want to do is implic...

6 Tage vor | 0

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Falkner-Skan code
You write: tau = (mu/(2*delta_y))*(4*un,2-un,3) But what des that mean to you? Is the fragment (4*un,2-un,3) intended to be...

6 Tage vor | 0

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sqrtm vs chol to produce draws the multivariate normal distribution
Don't bother. sqrtm also can have a similar problem, but you won't like what it does either! For example: A = rand(3,2); A = A...

7 Tage vor | 1

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How to get tangent line from a point not on the curve
The curve is: syms x y x0 F(x) = 945.75*x.^0.1002; A line tangent to the curve at any spcific location x0 would be simple to ...

8 Tage vor | 1

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Solving systems of trig equations
My gut says no symbolic solution will exist. But that does not mean my gut is accurate here. First, I would throw pencil and pap...

8 Tage vor | 0

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Merging piecewise polynomial (pp) structures
Is there any method to "merge" two PP functions? Well, no. Should there be one? I've been using and writing splines tools for 40...

8 Tage vor | 0

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Solve of implicity equations
alpha = 0.14; A = 3300; n = 0.01 ; b_2019 = 69100; rho = 0.02; uno_alpha_A = ((1-alpha)*A); dos_rho = (2+rho); uno_n = (1+n);...

8 Tage vor | 0

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What am I doing wrong?
ex2d is a function. You call a function, even a function you wrote yourself, by passing in arguments. For example, when you use ...

8 Tage vor | 0

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Why can't the index variable of a for loop be stored in a structure or other array?
Surely this is not a big problem? for ind = 1:10 status.ind = ind; % do Stuff end

9 Tage vor | 0

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is there any way to get a 2nd order polynominal through 2 points(each end point)
You want to fit a 2nd degree polynomial through two points? Of course only a straight line would work there through two points, ...

9 Tage vor | 1

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Is there an option to overwrite the old release when installing a new one?
I'll admit, I typically have 3 to 6 releases, and usually at the high end of that scale. They are useful to me in case I might w...

9 Tage vor | 0

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Volume of retinal lesion
It seems clear. You have multiple slices. Compute the area of each slice. At that point, you could just sum the area of each sli...

9 Tage vor | 1

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