Merge pull request #83 from JuliaLinearAlgebra/RA/omalled

Fix direct interpolation bug

Author: ranjanan

src/classical.jl

@@ -63,7 +63,7 @@ function direct_interpolation(At, T, splitting)
 
     Pp = rs_direct_interpolation_pass1(T, splitting)
     Px, Pj, Pp = rs_direct_interpolation_pass2(At, T, splitting, Pp)
-    R = SparseMatrixCSC(maximum(Pj), size(At, 1), Pp, Pj, Px)
+    R = SparseMatrixCSC(isempty(Pj) ?  0 : maximum(Pj), size(At, 1), Pp, Pj, Px)
     P = R'
 
     P, R

test/runtests.jl

@@ -322,3 +322,9 @@ for f in (smoothed_aggregation, ruge_stuben)
 end
 
 end
+
+# Issue #56
+X = poisson(27_000)+24.0*I
+ml = ruge_stuben(X)
+b = rand(27_000)
+@test solve(ml, b, reltol = 1e-10) ≈ X \ b rtol = 1e-10