Re: Dealing with submatrices

• To: mathgroup at smc.vnet.net
• Subject: [mg18157] Re: [mg18099] Dealing with submatrices
• From: "Wolf, Hartmut" <hwolf at debis.com>
• Date: Sat, 19 Jun 1999 23:54:25 -0400
• Organization: debis Systemhaus
• References: <199906171626.MAA20061@smc.vnet.net.>
• Sender: owner-wri-mathgroup at wolfram.com

```Hello Chris,

Chris Hall schrieb:
>
> I want to construct a 9x9 matrix using 9 existing 3x3 matrices:
> M = { {m11, m12, m13}, {m21, m22, m23}, {m31, m32, m33}}
>
> The problem is that this creates a too-deep nested list and I can't
> figure out how
> to make it a 9x9.  Flatten doesn't appear to be the right tool.
>
Perhaps what you need is something like that:

In[1]:= f[in_]:=With[{s=Flatten[Flatten/@ Transpose[#]& /@  in,1]},
If[Length[Dimensions[s]]>=2,s,
"incompatible dimensions at input"]
]

such that:

In[2]:= ma=Array[a,{3,2}];
In[3]:= mb=Array[b,{3,3}];
In[4]:= mc=Array[c,{1,4}];
In[5]:= md=Array[d,{1,1}];

In[6]:= f[{{ma,mb},{mc,md}}]
Out[6]= {{a[1,1],a[1,2],b[1,1],b[1,2],b[1,3]},
{a[2,1],a[2,2],b[2,1],b[2,2],b[2,3]},
{a[3,1],a[3,2],b[3,1],b[3,2],b[3,3]},
{c[1,1],c[1,2],c[1,3],c[1,4],d[1,1]}}

regards, hw

```

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