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Re: how to build pattern for a square matrix of reals?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg98487] Re: how to build pattern for a square matrix of reals?
  • From: m.r at inbox.ru
  • Date: Fri, 10 Apr 2009 04:59:26 -0400 (EDT)
  • References: <grhp95$mj7$1@smc.vnet.net>

sagra... at gmail.com wrote:
> As in subject: how to build a pattern that will specify that given
> argument of a function has to be square matrix of reals?  Tried with
> following for "square matrix" part:
>   f[x_?MatrixQ[#] && Dimensions[#][[1]] == Dimensions[#][[2]]
> &] := ...
> but it doesn't seem to be working...
>
> Thanks.

Regarding the type checking, a fast way to do that is to use MatchQ[#,
_Real]& as the test in MatrixQ. It is recognized as a special case and
for packed arrays it'll be O(1):

In[1]:= m = RandomReal[1, {4*^3, 4*^3}];

In[2]:= Timing[MatchQ[m, {{_Real..}..}]]

Out[2]= {0.906, True}

In[3]:= Timing[MatrixQ[m, MatchQ[#, _Real]&]]

Out[3]= {0., True}

Maxim Rytin
m.r at inbox.ru


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