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7.5.23.0. purityTriang
Procedure from library purityfiltration.lib (see purityfiltration_lib).

Usage:
purityTriang(S), S matrix with entries of an Auslander regular ring D

Return:
a matrix T

Purpose:
compute a triangular block matrix T, such that M=D^p/D^q(S^t) is isomorphic to M'=D^p'/D^q(T^t)

Example:
 
LIB "purityfiltration.lib";
ring D = 0,(x1,x2,d1,d2),dp;
def S=Weyl();
setring S;
int i;
matrix R[3][3]=0,d2-d1,d2-d1,d2,-d1,-d1-d2,d1,-d1,-2*d1;
print(R);
==> 0, -d1+d2,-d1+d2,
==> d2,-d1,   -d1-d2,
==> d1,-d1,   -2*d1  
matrix T=purityTriang(transpose(R));
// a triangular blockmatrix representing the module coker(R)
print(T);
==> 0, 1,1,-1, 0,  0, 0,  
==> -1,0,1,0,  -1, 0, 0,  
==> 0, 0,0,-d1,-d2,-1,0,  
==> 0, 0,0,-1, -1, 0, -1, 
==> 0, 0,0,0,  0,  1, -d2,
==> 0, 0,0,0,  0,  1, 0,  
==> 0, 0,0,0,  0,  0, d1  


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