Daniel Lichtblau

15,428 reputation

2052

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	location	Champaign, IL
	age	55
visits	member for	1 year, 4 months
	seen	yesterday
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	15,428 reputation	bio	website		visits	member for	1 year, 4 months
2052 badges		location	Champaign, IL		seen	yesterday

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1d	comment	How to get a solution set of a nonlinear system of equations? Can get a result if you restrict the space, e.g. try `Solve[{0 == y - 1/2 Tan[(\[Pi] x)/2], 0 == x - 1/2 Tan[(\[Pi] y)/2], -10 <= x <= 10, -10 <= y <= 10}, {x, y}]`
2d	comment	How to create new “person curve”? Ironically, it was Newton himself who was drawn above. In portrait form, suitable for hanging in ones quarters. But I digress.
2d	comment	How to create new “person curve”? Nice picture of Newton. But why does his shirt have so many buttons?
2d	answered	Solving an ODE in power series
May 16	comment	How to enumerate multisets What I meant was that you can order these sets in a particular way. Say the full set has length n and your subsets have length k. You can order so that the rth one is given by the digits, base n, of r-1. Just remember to use leading zeros, and to have the correspondende 0-> first element, 1->second element, .... (If this is still not clear, I can add an edit to show explicitly.)
May 15	answered	Creating a NearestFunction that returns an index
May 15	answered	How to enumerate multisets
May 15	comment	Minimizing a Matrix @J.M. I had intended: `Total[Abs[Flatten[cmat*mat]]]`, that is, no transposing. It is still a different problem in that I used `Abs` (and made mention of this). The reason was that otherwise I was getting results arnitrarily negative with matrix values that were huge. Whether that is acceptable or unexpected depends on the actual proble details of course; I was guessing it was not the anticipated result, and was guessing as to the needed adjustment to the problem specification.
May 15	comment	Upper bound for x `Maximize[{f[x],f[x]>0}, x]` is perhaps what you want.
May 14	comment	Solving for variables in a series of nonlinear equations Syntax for this would be `Solve[{(660 (-0.37 + b) (x - c))/(660 + a) - 0.37 c == y,...}, {a,b,c}]`. Note use of "==" (doubles equal sign) in the equation; a single one denoted Mathematica's `Set` which is not what you would want there.
May 14	awarded	Nice Answer
May 14	revised	Minimizing a Matrix method improvements
May 14	awarded	Nice Answer
May 14	comment	draw a graph of a polynomial function with variables in the denominator Could try setting options to make ContourPlot3D faster 9at risk of less accuracy). Or could try to define a region where \|f\|<epsilon, say, and do a region plot.
May 14	comment	Common subexpression from two expressions Not sure why it misses multiplying GCompile`$9Compile`$10 as a CSE. Overall it would save a multiplication if I am counting correctly.
May 13	comment	Minimizing a Matrix Okay. I'm still getting results that do not seem to be playing nicely with the code. Will have another look tomorrow.
May 13	comment	Minimizing a Matrix It seems quite unstable and can give hugely negative results when I change to account for pth roots. Is there any chance that the additive term was meant to be `lambda*Tr[mm.c.(Transpose[mm])]`? That seems to make it give plausible results quickly.
May 13	comment	Minimizing a Matrix Yes it does. Minimizing one is equivalent to minimizing the other (it's a monotonic function) but this change of mine messes up the result. Will edit accordingly.
May 13	answered	Minimizing a Matrix
May 13	answered	Common subexpression from two expressions