# John D'Errico

### Retired

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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transposing 3d matrix with permute function

You CANNOT tell MATLAB that a matrix is explicitly 265x508x1, and have it recognize that third singleton dimension. Yes, if you ...

circa 2 ore fa | 0

How to calculate are under the curve from 2 vector sets.

It seems as if you want to compute the area between the curve and the x axis, while ignoring the sign of y. But a simple integra...

circa 14 ore fa | 1

| accettato

lsqnonlin optimization: large condition number of Jacobian matrix at all iterations, but full rank

@SA-W - A full rank does NOT mean the parameters are not linearly dependent. With that high of a condition number, it often does...

circa 14 ore fa | 0

lsqcurvefit() moved from Matlab to toolbox?

You definitely mis-remember this. lsqcurvefit has always been in the optimization toolbox. At least as long as I can recall on t...

1 giorno fa | 0

Hi there, I am trying to solve a differentiation of long equation. The system shoot me the warning that cannot find a explicit solution. I need the value of X in terms C.

I want world peace. Does that mean I can have it? I even need world peace. Still, no good. How about you? You need to solve an e...

1 giorno fa | 0

| accettato

how to write a specific text in matlab

L appears there as a function ONLY as the inverse of L. As such, it is just a name. We could call it something else, and nothing...

1 giorno fa | 0

How to generate bivariate random normally distributed 3d array?

Um, trivial? You apparently want to generate 300 samples of a bivariate normal. So generate them as a 300x2 array, Then reshape...

2 giorni fa | 1

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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...

2 giorni fa | 0

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 ...

3 giorni fa | 0

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...

3 giorni fa | 0

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...

3 giorni fa | 0

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...

4 giorni fa | 0

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...

5 giorni fa | 0

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...

5 giorni fa | 0

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...

5 giorni fa | 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...

6 giorni fa | 0

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...

6 giorni fa | 1

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...

7 giorni fa | 0

| accettato

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...

7 giorni fa | 1

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...

7 giorni fa | 1

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 ...

7 giorni fa | 0

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...

8 giorni fa | 0

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...

8 giorni fa | 2

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...

8 giorni fa | 0

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...

8 giorni fa | 1

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...

10 giorni fa | 0

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...

11 giorni fa | 0

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...

11 giorni fa | 1

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...

12 giorni fa | 0

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...

12 giorni fa | 1

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