Community Profile # John D'Errico

### Retired

Last seen: Today Actif depuis 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. I won't do consulting by mail.

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Why the nonlinear least square fitted curve is not a curve?
Data=[0.928571429, 0; 0.012118074, 1.5; -0.450001188, 3; -0.316739249, 4.5; 0.394139277, 6; 0.094786629...

environ une heure il y a | 0

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vpa solving 5 equations with 5 unknowns, but result is an empty structure
Suppose I had two equations. Two unknowns. Totally trivial, but they are not unlike your question. x + y = 1 x - y <= 3 ...

environ 17 heures il y a | 0

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Second time derivative of ODE45 solution looks bumpy
Reemmber that the gradient function usues an APPROXIMATION. And, that at the ends of the series, that approximation is less good...

environ 22 heures il y a | 0

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How to plot a surface curve with inequalities?
And exactly what is the problem? I think what you do not understand is, what you have created is NOT a surface. M = 0.85 : 1/20...

1 jour il y a | 0

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Fsolve produces comlex numbers
Remember that fsolve does not allow constraints. Not even bound constraints. So when one of the variables tries to go into a bad...

2 jours il y a | 0

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Optimisation Algorithm and Levenberg-Marquardt for fitglm in MATLAB
The important thing you need to recognize is that fitglm fits a LINEAR model. No nonlinear iterations will be performed. fitgl...

2 jours il y a | 0

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error in the process of symbol operation of the matrix
Why do you think there is something wrong with T? We don't know why you wrote this code. It computes what you told MATLAB to com...

2 jours il y a | 0

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Is it possible to plot a curve with changing colours under a single plot?
Arguably, this is something the line function would allow you to do. But line allows you to specify only a single color for an e...

3 jours il y a | 0

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Find value at which a line changes its slope
There is NO exact point where that can be known to happen. Your curve is noisy. At best, you can estimate where the curve start...

3 jours il y a | 0

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How do I get random variables generated from a distribution in [-1, 1]?
The MATLAB crystal ball is foggy today. You give us a tiny fragment of code, and then tell us that something strange happens. PR...

3 jours il y a | 1

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Can Simulink use symbolic constants (syms x, y, z) or only numerical values (x=1, y=2, z=3) are accepted ?
NO. Simulink will NOT use symbolic parameters. Sorry. Simulink is essentially a numerical solver. It does not perform symbolic c...

4 jours il y a | 0

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three order complex coefficient polynomial root matlab
Another classic solution is to find the matrix that has the same eigenvalues as your polynomial has roots. Then use eig to compu...

5 jours il y a | 1

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Problem with making cash change
Now that you have an answer, I'll add one that is not solved the way you would do so, but using an ILP solver, so an Integer Lin...

5 jours il y a | 1

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How do I code for optimization of max volume of box?
It would arguably be a good time to learn about something called Lagrange multipliers. They allow you to build constraints into ...

5 jours il y a | 0

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write down a function
There is no "function". It sounds as if, given vectors x and h, you want to know what the function would have been, as if MATLAB...

5 jours il y a | 0

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Using find to determine equality not of scalars, but vectors
This is not really the province of find. Yes, you can break an egg with a hammer, but it is not really the right tool for the pu...

5 jours il y a | 2

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How to do a Taylor expansion with a matrix
You cannot compute the Taylor series of a constant. You CAN compute a Taylor series, and then evaluate it at that constant value...

5 jours il y a | 0

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Is it possible to truncate a vector to form one of lower dimension?
You have two choices. First, you can extract the elements you want. Or you can delete the elements you wnat to drop. For example...

6 jours il y a | 1

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Most efficient way to put vector on the off-diagonal of the blocks of a block matrix
The most efficient way? SPDIAGS. help spdiags For example, to create a 6x6 sparse matrix, with an upper and lower diagonal ele...

8 jours il y a | 0

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xy+y^5+3=0 My input is real x, from this implicit equation y will have both real and imag values for each x I want to plot a 3 D plot where z will represent imag y. Pleasehelp
Simple enough. Just do exactly what you asked. Remember the roots of a 5th degree polynomial will in general have no algebraic s...

8 jours il y a | 0

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How do I fit two data sets to each other?
This is a classic problem of calibration. You have two curves, one of which must be shifted (translated) to the other. In some c...

8 jours il y a | 1

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Pick a value with some probability
Please stop asking the same question. There is NO way to know what distribution any set of data comes from. You can use tools to...

9 jours il y a | 0

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Why is the calculated Rsquare different between the embedded fit function and the EzyFit function (from File Exchange)?
Do you understand that R^2 is not valid, when computed for a model with no constant term? Instead, I recall there are variations...

9 jours il y a | 1

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I wanna implement this function, but it says there is an syntax error..
What langiuage are you using when you end a function with the statement endfunction? Not MATLAB. As well, IF you had posted the...

10 jours il y a | 0

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non-numerical answer for solving complex non-linear equation
I think you do not understand how variables work in MATLAB. Variables are dynamically assigned. When you assign them as you have...

12 jours il y a | 0

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Can I use my student license for and at work?
I would guess the answer is technically no. But it is arguable either way as long as you remain a student, IF when you are on co...

13 jours il y a | 1

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A single precision matrix multiplication problem
Why are you confused? NEVER trust the least significant bits of a floating point number. The numbers in a are singles. So the l...

13 jours il y a | 3

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I am stuck in making the pentadiagonal matrix A
This sort of thing is a BAD idea: A = A+spdiags(s_vec, 0, (nx+1)*(ny+1), (nx+1)*(ny+1)); % Add s to the main diagonal of A XX_...

14 jours il y a | 0

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Find the derivative of a spline curve obtained using cscvn
No. There is no simple "function" of a spline. It is a mess of coefficients that by themselves are fairly meaningless to those w...

15 jours il y a | 0

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Fitting powerlaw between two points
Given two points exactly, thus: yx = [0.047 100; 0.0382 0.1933]; y1 = yx(:,1); x1 = yx(:,2); You want the power law cur...

15 jours il y a | 0

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