Community Profile # John D'Errico

### Retired

4,673 total contributions since 2006

Mainly retired from Eastman Kodak. (Of course, Kodak itself is now semi-retired. I don't think I had any influence in that.) I still write MATLAB code as I find something interesting, and I do attempt to write new tools to put on the File Exchange when I think I can make a contribution.

However, I DON'T answer direct e-mail questions, and I do NOT do homework. In general, your homework is YOUR problem, not mine. Please do NOT e-mail me with your homework problems or student projects. If I was willing to answer your questions, I would very rapidly become overwhelmed, because one question is never just one simple question.

When I'm not doing something with MATLAB, you might find me playing bridge, either in the club or online on BBO.

Professional Interests: MATLAB, numerical analysis, mathematical modeling

Avocational interests: Bridge, woodworking, woodturning

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Distinct sum of 3 variable which ranges between 1-255
As you recognize yourself, if you simply form the sum of three integers, you cannot then recover the original values. That infor...

4 hours ago | 0

How to initialize an array such that the values satisfies an equation
Too bad, in the sense that for smaller L, say on the order of 8 or so, this is not that difficult to do exactly. (I have written...

12 hours ago | 0

Solving non linear equations sytem
I would reduce this to a 2 variable problem first. That is, use equation 1 to solve for x1. x1 = b1/cos(a1 + x2) Likewise,...

18 hours ago | 1

sparse to gridded 3-D interpolation
First, should MATLAB use all of the CPU capability? That is difficult in what you are doing, becaue it is not easily parallelize...

21 hours ago | 0

Regularization for Non-linear fitting with fitnlm.
(Please don't add answers to make a comment. Use comments for that.) But how can you do a simple regularization on the coeffici...

1 day ago | 2

185k1*185k Matrix
Think of it like this: If all of the elements in that matrix are non-zeros, then you have 185000^2 ans = 3.4225e+10 So 3...

1 day ago | 0

A function to find prime number
Hey, you wrote some code! Credit for that. :-) But what did you do? function isPrime(number) tf=isprime(number); if tf==tru...

1 day ago | 0

Question about the tolerance of lsqcurvefit
This is not a problem of lsqcurvefit tolerance. Instead, see that the error makes a statement about INTEGRATION tolerances. That...

1 day ago | 0

I am trying to integrate IMU and GPS data to find roll of ground vehicle on the same road at different velocities. But, I am getting inconsistent results and an error at higher velocities (45mph) compared to lower velocities(25mph).
The singular matrix suggests why it is you are getting garbage, as once you have that, nothing will likely make any sense. Is th...

1 day ago | 0

Linspace with varying increment
The problem is, vendor provided software cannot work like that. You have descibed several cases of potential interest to you, fr...

3 days ago | 1

Linear Constraint based on two variables fmincon
Why, if you already have other inequality constraints, is this a question? And how you wrote it, using A is inconsistent with yo...

3 days ago | 1

I need to solve an equation involving squares and cubes.
You have many values for both d and p? Do you want to solve it for all combinations of d and p? Anyway, first, I would recogniz...

3 days ago | 0

decrease calculation accuracy to speed up running time
You essentially cannot do what you want, with one small caveat. That is, you canot arbitrarily tell MATLAB to do all computation...

3 days ago | 3

how to plot an ellipse having her equation?
First, learn how to write a function. fun = @(x,y) x.^2 / 25 + y.^2 / 9 - 1; Note the use of the .^ operators. They will be im...

3 days ago | 0

Unable to predict data well enough
I would point out that your code shows you using the first SEVEN data points, not the first 10, despite your claim otherwise. n...

4 days ago | 0

how can i find the intersection point between the vertical lines and the curve (xmin,ymin) ?
The red curve is a piecewise linear interpolation, not really a curve, just connect the dots by the plotting routine. The green...

4 days ago | 1

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lsqcurvefit: is the output of this function unique for a given set of initial conditions (and deterministic model)?
The problem is, that is not your code. Not all of it. That is just how you call lsqcurvefit. We do not see the pandemic1Dall2 co...

4 days ago | 1

change a logical array value based on the index of another matrix
If you want to create x on the fly, then just do this: x = A > 4; If you for some reason really want to modify an existing vec...

5 days ago | 0

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What's the meaning of instrucment sound in Matlab?
Let me just answer this as if you asked for an explanation of what a sound is in the world of MATLAB. For example, if we try: l...

5 days ago | 0

vector to upper and lower triangular matrix
What you fail to see is that while your code works for a 3x3 matrrix, it must always fail for any n other than n==3. You want t...

5 days ago | 0

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double differentiation and double integration of sine wave
This is not a question about MATLAB, just understanding some basic mathematics. At least, understanding calc 101. First, you ne...

6 days ago | 0

Diagonal/Symmetric matrix
I don't even think your code works for a 3x3 matrix. The matrix it produces is OD OD = 81 23 18....

6 days ago | 0

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How do I open a pcode (.p) file created in a version older than MATLAB R2007b? My Matlab version is R2018b.
You cannot edit a .p file, if that is what you mean by open. That is true in any version. If the .p file is too old, but you s...

7 days ago | 0

How to transfer a Matlab toolbox I have in my machine to the machine of a colleague ?
If this is a toolbox that you have purchased from Mathworks, you cannot give it to someone else. If this is a toolbox you have ...

7 days ago | 0

For loop for matrix division
Why would you want to use any loop at all? For example, if A is an mxn matrix, and V is a vector of size mx1, then consider what...

8 days ago | 0

Can someone explain the concept of B= null(A) in simple words?
Think of A as a vector pointing someplace in a 5 dimensional space. Got that? It points somewhere. Now, in 5 dimensions, we co...

9 days ago | 1

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How to get more decimal places in my output?
In fact, it does NOT neglect that term. It is in there, just too small for you to see in only 4 decimal places. help format Yo...

9 days ago | 1

How to remove last characters from String using mod?
It is generally a bad idea to use names for variables that are already useful function names. So here rem is one such bad idea. ...

10 days ago | 2

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Random sampling of elements from an array based on a target condition in MATLAB
Are you looking for an exact match to V1? An approximate sum equal to V1? If so, then how close of a tolerance do you need? Is ...

11 days ago | 1