Re: expressions list -> equations list

*To*: mathgroup at smc.vnet.net*Subject*: [mg83997] Re: expressions list -> equations list*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Thu, 6 Dec 2007 02:49:06 -0500 (EST)*Organization*: The Open University, Milton Keynes, UK*References*: <fj6404$em9$1@smc.vnet.net>

Hauke Reddmann wrote: > 1st of all THX to all who answered my last question. Just one other before > I lend a Mathematica manual from the public lib and pester you no more :-) > > So. Now that I have a tensor it must vanish identically. I Flatten[] it first > and then I have a list of equations...oh, stop, I haven't. REDUCE (if I may > mention the name of a competition :-) could take a Solve[] now because it > automatically assumes a "=0" as default but Mathematica is anally-retentive > (a good thing :-) and I somehow must turn {a,b,c} into {a=0,b=0,c=0}. > Convert to string, global change "," -> "=0," and "}" -> "=0}", reconvert > to list? Is that possible? Or is there a less LISP-hack-style solution? The following examples, all using pure functions --- equivalent to anonymous functions in LISP, should fulfill your needs. lst = {a, b, c}; Thread[# == Table[0, {Length@#}]] &@lst Thread[# == Array[(0 &), Length@#]] &@lst Thread[# == ConstantArray[0, Length@#]] &@lst Cases[lst, x_ -> Equal[x, 0]] (* Each expressions yield {a == 0, b == 0, c == 0} *) lst = {x^2, Sin[x]^2 + Cos[x]^2, (x + 1)/x}; Thread[# == Table[0, {Length@#}]] &@lst Thread[# == Array[(0 &), Length@#]] &@lst Thread[# == ConstantArray[0, Length@#]] &@lst Cases[#, x_ -> Equal[x, 0]] &@lst (* Each of the above expression returns 2 2 2 1 + x {x == 0, Cos[x] + Sin[x] == 0, ----- == 0} x *) Regards, -- Jean-Marc