*Matrix witihn matrix*

• To: mathgroup at yoda.physics.unc.edu
• Subject: *Matrix witihn matrix*
• From: "Roger M. Jones" <rmj at llewelyn.slac.stanford.edu>
• Date: Fri, 24 Jun 1994 18:16:55 -0700

```I have a matrix containing sub-matrices which I wish to combine.

I have implemented this as:

CatMatrix[a_,b_,c_,d_]:=Block[{t1},
t1=Length[a];Join[Table[Flatten[{a[[i]],b[[i]]}],
{i,1,t1}],Table[Flatten[{c[[i]],d[[i]]}],
{i,1,t1}]]].

So that:

a={{a11,a12,a13},{a21,a22,a23},{a31,a32,a33}};
b={{b11,b12,b13},{b21,b22,b23},{b31,b32,b33}};
c={{c11,c12,c13},{c21,c22,c23},{c31,c32,c33}};
d={{d11,d12,d13},{d21,d22,d23},{d31,d32,d33}};

{a,b,c,d}----->

{{a11, a12, a13, b11, b12, b13}, {a21, a22, a23, b21, b22, b23},

{a31, a32, a33, b31, b32, b33},

{c11, c12, c13, d11, d12, d13},

{c21, c22, c23, d21, d22, d23}, {c31, c32, c33, d31, d32, d33}}

Does anyone know of a  simplier implementation?

```

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