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Math Forum » Discussions » sci.math.* » sci.math.num-analysis.independent

Topic: Binary or Logical Selection : Given an array A and a binary or
logical vector S, how do I select the rows of A when S = 1 or True ?
Replies: 6   Last Post: Sep 24, 2012 5:42 AM

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dr.beauwebber@googlemail.com

Posts: 7
Registered: 9/22/12
Re: Binary or Logical Selection : Given an array A and a binary or
logical vector S, how do I select the rows of A when S = 1 or True ?
Posted: Sep 23, 2012 5:57 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply


>
> If A is n by 3 and S is an n-vector, then define a selection matrix,
>
> say T, as those rows of an n by n identity matrix for which the
>
> corresponding element of S is 1. Then R = TA contains the
>
> coordinates of the points you want. (Yes, I realize that might be
>
> seen as cheating, because we haven't expressed T as a function of
>
> S using standard operators. If we could, we wouldn't need T!)

Ah, I think that I understand that.
I have to start with S as I have spent various lines defining it, then,
I think I can say :
T ij = 0
Tii = Si
R = TA

Something like that ?
cheers,
Beau

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