John D'Errico

Retired

Last seen: Today | Active since 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.

Statistics

All

View badges

Content Feed

Answered
Does the randi function have a good level of pseudorandomness?
randi is random. At least as good as is mathematically possible to make it so, based on the random number generation tools we ha...

13 hours ago | 1

Answered
Integral of user-defined function
Is your code vectorized? That is, what happens when a VECTOR of elements for y is passed in? (It does not appear to be.) integ...

1 day ago | 0

Answered
I want to find second and third maxima in a row of a matrix of size 1000*8
BREAK DOWN PROBLEMS THAT ARE TOO LARGE FOR YOU TO HANDLE INTO SMALLER, BITE SIZED CHUNKS. First, if it is a particular row, the...

1 day ago | 0

Answered
How to get area between 2 cdf curves?
If the curves cross, then you need to decide what the "area between" means. That is, is the area in one part negative? Or do you...

2 days ago | 0

Answered
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 ...

3 days ago | 0

Answered
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...

3 days ago | 1

| accepted

Answered
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...

4 days ago | 0

Answered
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...

4 days ago | 0

Answered
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...

4 days ago | 0

| accepted

Answered
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...

5 days ago | 0

Answered
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...

5 days ago | 1

| accepted

Answered
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...

5 days ago | 0

Answered
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 ...

6 days ago | 0

Answered
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...

6 days ago | 0

Answered
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...

6 days ago | 0

Answered
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...

7 days ago | 0

Answered
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...

8 days ago | 0

Answered
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...

8 days ago | 0

Answered
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...

8 days ago | 0

| accepted

Answered
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...

8 days ago | 0

Answered
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...

8 days ago | 1

Answered
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...

9 days ago | 0

| accepted

Answered
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...

10 days ago | 1

Answered
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...

10 days ago | 1

Answered
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 ...

10 days ago | 0

Answered
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...

10 days ago | 0

Answered
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...

11 days ago | 2

Answered
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...

11 days ago | 0

Answered
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...

11 days ago | 1

Answered
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...

13 days ago | 0