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MathGroup Archive 1997

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Re: (Q:) ReplacePart + SubMatrix replacement

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7066] Re: [mg7033] (Q:) ReplacePart + SubMatrix replacement
  • From: Allan Hayes <hay at haystack.demon.co.uk>
  • Date: Sat, 3 May 1997 22:04:56 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Fri, 2 May 1997
"m.r." <schaferk at communique.net>
[mg7033] (Q:) ReplacePart + SubMatrix replacement

> For A,B n-by-n,  matrices,
> K  non empty subset of CartesianProduct[Range[n],Range[n]]...
> i wish to replace the block A[[K]] with the block B[[K]]

As you comment in your full message (copied below ****) ReplacePart  
does not seem to perform as expected.
However:

A = Table[0,{3},{3}]
	{{0,0,0},{0,0,0},{0,0,0}}
B = Table[1,{3},{3}]
	{{1,1,1},{1,1,1},{1,1,1}}
A[[{1,3},{2,3}]] = B[[{1,3},{2,3}]];
A
	{{0,1,1},{0,0,0},{0,1,1}}
	
Of course, much more is possible using this technique
	
Allan Hayes
hay at haystack.demon.co.uk
http://haystack.demon.co.uk
*********************************

Begin forwarded message:

>From: "m.r." <schaferk at communique.net>
>To: mathgroup at smc.vnet.net
>Subject: [mg7033] (Q:) ReplacePart + SubMatrix replacement
>Organization: Communique Inc.

greetings:

Mma3.0 has added a form of ReplacePart not found in Mma2.2.2:

?ReplacePart[expr,new,pos,npos]

ReplacePart[expr,new,pos,npos] replaces parts at positions pos
	in expr by parts at positions npos in new.

For
A,B n-by-n,  matrices,
K  non empty subset of CartesianProduct[Range[n],Range[n]]

one can use

ReplacePart[A,B,K,{1,1}]

to replace the block A[[K]] with B[[1,1]]. (no problem)

what i wish ( though perhaps unrealistically) is

for

ReplacePart[A,B,K,K]

to replace the block A[[K]] with the block B[[K]].

am i misreading the above usage message for ReplacePart?

if so, how does one do a simple block replace in "one fell swoop"?

sincerely.

m. r.

email replies to

schaferk at tennessee.nrlssc.navy.mil



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