Re: Trouble with a system of equations

*To*: mathgroup at smc.vnet.net*Subject*: [mg77596] Re: Trouble with a system of equations*From*: Yaroslav Bulatov <yaroslavvb at gmail.com>*Date*: Wed, 13 Jun 2007 07:42:36 -0400 (EDT)*References*: <f4lb44$fvv$1@smc.vnet.net>

On Jun 11, 10:31 pm, Ray Koopman <koop... at sfu.ca> wrote: > On Mon, 11 Jun 2007 07:38:00 -0500 drmajor... at bigfoot.com wrote: > > > There's an unmatched bracket in > > >> m = Inverse[ Subsets[Times@@#]& /@ Tuples[{0,1},k]] ]. > > > and I haven't found a way (so far) to correct it so that the code works. > > > Bobby > > Ah, the joys and perils of posting code without testing it first. > Maybe someday I'll get Mathematica for my machine at home. > > Aside from the extra ], that must must have been teleported from > LinearSolve[x,Log[p/(1-p)], where a ] is missing, the problem is > that I simply copied the form of an example in the Subsets online > documentation, with h changed to Times, not realizing that Times@@# > would be evaluated before Subsets got to it. > > Here are two ways to get x: > > ReleaseHold@Subsets[Hold@Times@@#]& /@ Tuples[{0,1},k] > > or (preferably, I think) > > Times@@@Subsets@#& /@ Tuples[{0,1},k]. > > With[{k = 2}, Inverse[ Times@@@Subsets@#& /@ Tuples[{0,1},k] ]] > > {{ 1, 0, 0, 0}, > {-1, 0, 1, 0}, > {-1, 1, 0, 0}, > { 1,-1,-1, 1}} > > With[{k = 3}, Inverse[ Times@@@Subsets@#& /@ Tuples[{0,1},k] ]] > > {{ 1, 0, 0, 0, 0, 0, 0, 0}, > {-1, 0, 0, 0, 1, 0, 0, 0}, > {-1, 0, 1, 0, 0, 0, 0, 0}, > {-1, 1, 0, 0, 0, 0, 0, 0}, > { 1, 0,-1, 0,-1, 0, 1, 0}, > { 1,-1, 0, 0,-1, 1, 0, 0}, > { 1,-1,-1, 1, 0, 0, 0, 0}, > {-1, 1, 1,-1, 1,-1,-1, 1}} OK that works, thanks. One problem with the original system is that I set up the estimation equations in terms of E[x_i y] (assuming uniform distribution over x's), and not empirical odds ratios which apparently make it much harder to solve (Andrzei's solution works fine for 2 variables, but takes too long for 3)

**Follow-Ups**:**Re: Trouble with a system of equations***From:*Yaroslav Bulatov <yaroslavvb@gmail.com>

**Re: Re: Trouble with a system of equations***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>