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function res=%sp_norm(S,flag)
// Copyright INRIA
[lhs,rhs]=argn(0)
if rhs==1 then flag=2;end //norm(S)=norm(S,2)
[m,n]=size(S)
if m==1|n==1 then //vector norm
[ij,v]=spget(S);
res=norm(v,flag);
return
end
select flag
case 1 then
res=maxi(ones(1,m)*abs(S))
case 2 then
if m<n then
S=S*S'
elseif m>n then
S=S'*S
end
tol=1.d-5;
x = sum(abs(S),1)';
res = norm(x);
if res==0 then return,end
x = x/res;res0 = 0;
while abs(res-res0) > tol*res
res0 = res; Sx = S*x; res = norm(Sx);
x = S'*Sx;
x = x/norm(x);
end
if m<>n then res=sqrt(res),end
case %inf then
res=maxi(abs(S)*ones(n,1))
case 'inf' then
res=maxi(abs(S)*ones(n,1))
case 'fro' then
[ij,v]=spget(S);
res=sqrt(sum(abs(v.*v)))
else
[ij,v]=spget(S);
res=norm(v,flag);
end
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