718 reputation
2526
bio website
location Seattle, WA
age 70
visits member for 2 years
seen 11 hours ago

I retired in 2006 and bought Mathematica and a stack of math books with the goal to teach myself to become a world-class mathematician. I am on pace to achieve that goal sometime shortly after the next Ice Age.

I consider myself a Mathematical Mutt (no papers) who occasionally ventures off the back porch to play in the yard with the big dogs.

I donate regularly to the The OEIS Foundation.

When I look at the patterns, I can hear the wheels turning. When I look at the math, I find out the hamsters have died.


Apr
17
comment Why the complicated pattern in this 3D plot?
@Kuba, perfect! Make it an answer and I'll sign off.
Feb
15
comment Conditionally replace rows in lists
@kguler, I was tormented by a simple replacement problem until I found your answer. The _? was the key. b /. _?(1 < # &) :> 0 Thanks for the help.
Feb
11
comment Using Reduce on an inequality
@rasher, looks good. Is there any way to explain the steps?
Feb
2
comment Question about inequality plot
@murray, the plot expression is from WA
Oct
3
comment How to optimize computing a product?
Possible duplicate mathematica.stackexchange.com/q/26732/973
Aug
5
comment Can we compile using only Integers Of Unusual Size?
@kirma, make that an answer and I will accept it.
Jul
31
comment Collatz Tool Box — any speed ups possible?
@OleksandrR., also the $10^{477119}$ number is calculated in omegaSubOrbit[x] with x being the uniqueRank number. Both calculations are very quick--under 2 seconds.
Jul
31
comment Collatz Tool Box — any speed ups possible?
@OleksandrR.,no, I use my short-cut, which is what this is all about. Notice these numbers from the example: $4805005, 1903828$. The first is the count of multiplies required to get down to $1$ and the second is the number of sub orbits processed to get to that number. Each sub orbit contains its own length, so the first sub orbit adds $1000000$ to the count and moves on to the next sub orbit. So, the whole thing is done with a series of additions. The key is: IntegerExponent[x+1,2] applied to the first number of the sub orbit provides that count.
Jul
31
comment Collatz Tool Box — any speed ups possible?
@cormullion, and I had to show all the code because if you tweak one function, most likely you would have to tweak another to keep everything working together.
Jul
31
comment Collatz Tool Box — any speed ups possible?
@cormullion, Because I'm an old procedural programmer, I feel most comfortable using For and While and I don't usually see how to eliminate them. This post is two-fold---One, to let others grab this stuff and play with it and Two, to find out how to speed up the countOrbit function to maybe get it below 10 minutes duration on my pc.
Jul
12
comment Building graph based on the cities connection?
@rm-rf, I assumed that since he is selecting cities by population, and if he wanted one point in each state, then the resultant graph would have the most populus city of each state as the location of its vertex. I had used this approach on the travelling salesman problem 30-years ago (without any more success than the other methods.)
Jul
12
comment Building graph based on the cities connection?
Imagine a light-house with its revolving light at each city. When the light hits another city, draw the line, unless that line crosses another. The bottom graph has no crossing lines. (i.e., it's planar.) That's the best I can do to help.
Jul
12
comment Building graph based on the cities connection?
Bottom graph is most populus city in each state. Then there is a pruning algorithm to reduce the number of edges.
Jun
22
comment Trace of FullSimplify
I put a ( before the 2b and a ) before the / on the second line, which made only one fraction.
Jun
22
comment Trace of FullSimplify
The reason I asked, is that I broke it down into smaller chunks to try the simplify and got a different answer. (I was treating the entire thing as a fraction, which is not how it is stated.)
Jun
22
comment Trace of FullSimplify
What did you get manually?
Jun
21
comment Can I run calculations on an external ssh server that doesn't have Mathematica installed?
It would depend on your license with Wolfram. My license allows two copies, work and home. And, while I only have one installed, I can launch two copies in the same computer, but no more than that.
Jun
17
comment Wallis Formula and Pippenger Product---How do we get symbolic output?
The observation about the discontinuities is the answer.
Jun
13
comment Wallis Formula and Pippenger Product---How do we get symbolic output?
+1 for the great analysis. I'm reviving hamsters as I write this. The link to Pippenger in the OP has something similar for the $n$th steps.
Jun
12
comment Wallis Formula and Pippenger Product---How do we get symbolic output?
@CoreyKelly, I put the results into the OP, so it is more easily read.