Rank: 4 based on 3185 downloads (last 30 days) and 52 files submitted
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John D'Errico

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Retired

Personal Profile:

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, but I DON'T answer your questions, and I do NOT do homework. Your homework is YOUR problem, not mine. Do NOT e-mail me with your homework problems or student projects. When I'm not doing something with MATLAB, you might find me playing bridge.

Professional Interests:
Bridge, MATLAB, numerical analysis, mathematical modeling

 

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Files Posted by John View all
Updated   File Tags Downloads
(last 30 days)
Comments Rating
23 May 2014 Screenshot A suite of minimal bounding objects Suite of tools to compute minimal bounding circles, rectangles, triangles, spheres, incircles, etc. Author: John D'Errico miminum, bound, bounding, circle, rectangle, triangle 93 16
  • 4.66667
4.7 | 6 ratings
29 Apr 2014 polyfitn Polynomial modeling in 1 or n dimensions Author: John D'Errico polyfit, modeling, regression, linear regression, approximation, function 264 43
  • 4.96
5.0 | 25 ratings
29 Apr 2014 Screenshot SLM - Shape Language Modeling Least squares spline modeling using shape primitives Author: John D'Errico spline, splines, cubic, hermite, breaks, knots 146 103
  • 5.0
5.0 | 52 ratings
29 Jan 2014 Moving window standard deviation A (fast) windowed std on a time series Author: John D'Errico standard deviation, std, window, filter, movingavg 109 16
  • 4.72727
4.7 | 11 ratings
30 Oct 2013 HPF - a big decimal class High precision floating point arithmetic, a new class written in MATLAB Author: John D'Errico hpf, multiple precision, big decimal, floating point, arithmetic, mathematics 44 17
  • 5.0
5.0 | 8 ratings
Comments and Ratings by John View all
Updated File Comments Rating
20 Sep 2014 Trigonometric function errors around pi or pi/2, sin(pi) or cos(pi/2) The constant pi in matlab is a floating-point approximation of 'pi'. There is a remedy for it! Author: Sung-Eun Jo

If, in your case, A is a diagonal matrix, why do you think you need to compute an eigen-decomposition to compute the matrix exponential? That alone will cause unwanted numerical trash to accumulate.

20 Sep 2014 Trigonometric function errors around pi or pi/2, sin(pi) or cos(pi/2) The constant pi in matlab is a floating-point approximation of 'pi'. There is a remedy for it! Author: Sung-Eun Jo

This is just a confusing set of tools, with very little purpose behind them.

Matrix exponentials, with degree input versus radians? Are you kidding? Perhaps you misunderstand what a matrix exponential is, or what it is used for. Anyway, there is already a function in MATLAB called EXPM, which does a very credible job for the purpose. And since it was Cleve who wrote the paper called "19 Dubious Ways to Compute the Matrix Exponential", maybe they know how to solve the problem in general.

As far as sin_rad goes, it is simply better to learn about floating point arithmetic and how to deal with it than to worry about whether sin(pi) returns a non-zero.

While the functions do have help in them, the tools themselves are just a silly idea.

05 Sep 2014 Variable Precision Integer Arithmetic Arithmetic with integers of fully arbitrary size. Arrays and vectors of vpi numbers are supported. Author: John D'Errico

Of course it is free. The file exchange provides tools that are free for your use. VPI does not come with MATLAB directly because it was written by a third party. In this case, I am that third party.

Just download it, install it as directed, then use it and enjoy it.

30 Aug 2014 Surface Fitting using gridfit Model 2-d surfaces from scattered data Author: John D'Errico

For those of you who don't appreciate why Felon's comment is silly, think of it like this. Gridfit fits a surface of the form f(x,y), over a rectangular grid. It does so quite well, as many people have found over the years.

While you may think of the surface of a sphere as a surface, it is not of the form that gridfit can fit. It is multi-valued, so for any single (x,y) pair, there will be zero, one, or two values of z that would apply. As well, that "surface" (better to call it a manifold) has derivative singularities, if we were to look at it as a function of x and y. So even a hemisphere will be problematic for this tool.

You would not use gridfit to fit something that is not representable as a function of two variables over a rectangular grid, any more than you would expect it to do numerical integration, numerical optimization, or compute an FFT. Nor would you expect it to cook dinner for you, do your laundry, etc. Use the right tool to solve your problem, but if you try to force the wrong tool to solve a random problem, expect poor results and don't complain about what you get.

29 Aug 2014 Surface Fitting using gridfit Model 2-d surfaces from scattered data Author: John D'Errico

Felon -

So you are using a tool that builds a single valued function to fit something that is obviously not. What did you expect? Magic?

Software does what it is programmed to do. It does not magically rewrite itself when you give it a problem of a completely different sort. In fact, I fail to understand why you would downrate a tool for not solving a class of problem it is explicitly not designed to solve.

If you have a closed manifold, like a ball or some other multivalued form, then don't use this tool. I have NEVER claimed it would solve that problem. Instead, you might look into tools like convex hulls, alpha shapes, CRUST, etc. Or, you might choose to convert the problem into spherical coordinates, at which point gridfit would be able to build a viable surface.

Or maybe you just wanted to complain with no good reason.

Comments and Ratings on John's Files View all
Updated File Comment by Comments Rating
20 Sep 2014 Surface Fitting using gridfit Model 2-d surfaces from scattered data Author: John D'Errico Jacob

I wish I could remove my previous question, 2 seconds on google pointed me to Matlab's interp2 which I'm using now on the output of your excellent gridfit. Thanks for sharing!

20 Sep 2014 Surface Fitting using gridfit Model 2-d surfaces from scattered data Author: John D'Errico Jacob

I found that it is very straightforward to fit a nice looking surface to some 55 data-points using gridfit. I was wondering though, is there a way to get values of the surface that are not on the nodes? I wish to interpolate between my 55 samples using the surface.

20 Sep 2014 Surface Fitting using gridfit Model 2-d surfaces from scattered data Author: John D'Errico Jacob

05 Sep 2014 Variable Precision Integer Arithmetic Arithmetic with integers of fully arbitrary size. Arrays and vectors of vpi numbers are supported. Author: John D'Errico D'Errico, John

Of course it is free. The file exchange provides tools that are free for your use. VPI does not come with MATLAB directly because it was written by a third party. In this case, I am that third party.

Just download it, install it as directed, then use it and enjoy it.

05 Sep 2014 Variable Precision Integer Arithmetic Arithmetic with integers of fully arbitrary size. Arrays and vectors of vpi numbers are supported. Author: John D'Errico Wagenman, Seth

Is this free to download? R2014a which I am using does not have vpi apparently...

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