More troubles coming from indexed variables
- To: mathgroup at smc.vnet.net
- Subject: [mg25000] More troubles coming from indexed variables
- From: Barbara DaVinci <barbara_79_f at yahoo.it>
- Date: Fri, 1 Sep 2000 01:09:33 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Cari MathGrouppisti
Some time ago a post of mine just concerned indexed
variables.
(I had replies, kind an learned, from many persons -
Matthias Bode, David Keith, Steven M. Christensen,
Otto Linsuain and Hartmut Wolf.
I thank them all.)
Now an even worse trouble is running.
I'm writing an educational notebook
on least-square fit and in a subsection I must show
how the well-known
formula is carried out.
This provides a symbolic data set :
datsimx = Table[x[k], {k, 1, 10}]
datsimy = datsimx /. x -> y
{x[1], x[2], x[3], x[4], x[5], x[6], x[7], x[8], x[9],
x[10]}
{y[1], y[2], y[3], y[4], y[5], y[6], y[7], y[8], y[9],
y[10]}
Now I must declare x[1] ... x[10] and y[1] ... y[10]
to be costants
(otherwise D[] and Dt[] ...) .
I tried two ways, both ineffective.
(I)
-----------------------------------------------------
SetAttributes[SetAttributes, Listable];
SetAttributes[datsimx, Constant];
SetAttributes[datsimy, Constant];
but I get
Attributes[datsimx]
{Constant}
Attributes[datsimx[[1]]]
Attributes::ssle: Symbol, string, or
HoldPattern[symbol]
expected at position 1 in Attributes[datsimx[[1]]]
I suppose that is because
Head[datsimx[[1]]]
x
instead of
Head[datsimx[[1]]]
Symbol
Therefore I'm not surprised seeing
SetAttributes[#, Constant] & @ datsimx
fails too.
(II)
-----------------------------------------------------
I definded this function
f[x_] := ToExpression[
StringJoin[
"Symbol[", ToString[x], "]"
]
]
SetAttributes[f, Listable]
whose aim is make x[i] "Symbol headed" ("so doing,
maybe, SetAttributes stops shouting its warning
messages", I deceived myself)
But f[datsimx] make me howling with pain again:
Symbol::string: String expected at position 1 in
Symbol[x[1]].
Symbol::string: String expected at position 1 in
Symbol[x[2]].
Symbol::string: String expected at position 1 in
Symbol[x[3]].
General::stop: Further output of Symbol::string will
be suppressed during this calculation.
(This message is rather unclear to me)
-------------------------------------------
Please, is there a way to get out alive ?
-------------------------------------------
Affettuosi saluti
(The above is an Italian idiom meaning something like
"yours sincerely")
Barbara Da Vinci
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