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Piecewise once more

  • To: mathgroup at smc.vnet.net
  • Subject: [mg109219] Piecewise once more
  • From: Peter Breitfeld <phbrf at t-online.de>
  • Date: Sat, 17 Apr 2010 06:05:41 -0400 (EDT)

When trying to find an answer to mercia's post I came into this


stepFunction::usage =
  "stepFunktion[x,{x1,x2,...,xn},valfunc] generates a \
stepfunction using Piecewise from List xi, where x1<x_2<...xn
  valfunc is a function of two parameters to calculate the value \
inside Interval [\!\(\*SubscriptBox[\"x\", \
\"i\"]\),\!\(\*SubscriptBox[\"x\", 
RowBox[{\"i\", \"+\", \"1\"}]]\)]." ;

stepFunction[x_, mesh_List, valfunc_] :=
 Module[{args, bed, werte, part},
  part = Partition[mesh, 2, 1];
  werte = valfunc @@@ part;
  bed = (#1 <= x < #2) & @@@ part;
  args = Transpose[{werte, Flatten[bed]}];
  Evaluate[Piecewise[Evaluate@args]]]

treppe[y_]=stepFunction[y, mesh,(#1+#2)/2&]  

I get the warning:
Piecewise::pairs: The first argument of args$706 of Piecewise is not a
list of pairs.

But the output is ok and test like

treppe /@Range[1,20]

show the right result. A Plot works fine

What's wrong in my code to produce the message?

$Version= 7.0 for Mac OS X x86 (64-bit) (February 19, 2009)

-- 
_________________________________________________________________
Peter Breitfeld, Bad Saulgau, Germany -- http://www.pBreitfeld.de


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