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function g=mat_2_graph(a,directed,mat)
// Copyright INRIA
[lhs,rhs]=argn(0)
if rhs==2 then
mat='node-arc'
else
if rhs<>3 then error(39), end
end
// directed
if directed<>1&directed<>0 then
error('Second argument must be 0 or 1')
end
// a
if type(a)<>5 then
error('Matrix must be sparse')
end
[ij,v,mn]=spget(a);
n=mn(1)
m=mn(2)
// node-arc matrix
if mat=='node-arc' then
if prod(size(v))<>2*m then
error('Matrix has wrong number of elements')
end
if directed==1 then
if norm(ones(1,n)*a)<>0 then
error('Matrix is not a node-arc matrix')
end
itab=find(v==1)
jtab=find(v==-1)
if prod(size(itab))<>prod(size(jtab)) then
error('Matrix is not a node-arc matrix')
end
he=ij(itab,:); ta=ij(jtab,:)
[s,k]=sort(he(:,2)); he=he(k,:); he=he(:,1)
ma=prod(size(k)); he=he(ma:-1:1)
[s,k]=sort(ta(:,2)); ta=ta(k,:); ta=ta(:,1)
ma=prod(size(k)); ta=ta(ma:-1:1)
g=make_graph('foo',1,n,he',ta')
else
oa=ones(1,n)*a
if max(oa)>2|min(oa)<2 then
error('Matrix is not a node-arc matrix')
end
[ijp,vp,mnp]=spget(a');
s=size(ijp)
he=ijp(2:2:s(1),2)
ta=ijp(1:2:s(1),2)
g=make_graph('foo',0,n,he',ta')
end
elseif mat=='node-node'
// node-node matrix
if m<>n then error('Matrix must be a square matrix'), end
if min(v)<>1|max(v)<>1 then
error('Matrix is not a node-node matrix')
end
if directed==1 then
he=ij(:,1); ta=ij(:,2);
g=make_graph('foo',1,n,he',ta')
else
ij=spget(tril(a)');
he=ij(:,1); ta=ij(:,2);
g=make_graph('foo',0,n,he',ta')
end
else
error('Third argument must be ""node-node"" or ""node-arc""')
end
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