Ensure that colstop/rowstop are ≥ 0

Author: dlfivefifty

src/BandedMatrices.jl

@@ -372,14 +372,14 @@ end
 
 # start/stop indices of the i-th column/row, bounded by actual matrix size
 @inline colstart(A, i::Integer) = max(i-bandwidth(A,2), 1)
-@inline  colstop(A, i::Integer) = min(i+bandwidth(A,1), size(A, 1))
+@inline  colstop(A, i::Integer) = max(min(i+bandwidth(A,1), size(A, 1)), 0)
 @inline rowstart(A, i::Integer) = max(i-bandwidth(A,1), 1)
-@inline  rowstop(A, i::Integer) = min(i+bandwidth(A,2), size(A, 2))
+@inline  rowstop(A, i::Integer) = max(min(i+bandwidth(A,2), size(A, 2)), 0)
 
 @inline colstart(A::BandedMatrix, i::Integer) = max(i-A.u, 1)
-@inline  colstop(A::BandedMatrix, i::Integer) = min(i+A.l, size(A, 1))
+@inline  colstop(A::BandedMatrix, i::Integer) = max(min(i+A.l, size(A, 1)), 0)
 @inline rowstart(A::BandedMatrix, i::Integer) = max(i-A.l, 1)
-@inline  rowstop(A::BandedMatrix, i::Integer) = min(i+A.u, size(A, 2))
+@inline  rowstop(A::BandedMatrix, i::Integer) = max(min(i+A.u, size(A, 2)), 0)
 
 @inline colrange(A, i::Integer) = colstart(A,i):colstop(A,i)
 @inline rowrange(A, i::Integer) = rowstart(A,i):rowstop(A,i)

test/runtests.jl

@@ -391,7 +391,7 @@ for S in (view(A,:,:),view(B,1:10,:),view(C,:,1:10),view(D,1:10,1:10),
 end
 
 
-# negative bands
+## negative bands
 
 for A in (brand(3,4,-1,2),brand(5,4,-1,2),
             brand(3,4,2,-1),brand(5,4,2,-1))
@@ -405,7 +405,14 @@ for A in (brand(3,4,1,2),brand(3,4,-1,2),brand(3,4,2,-1)),
     @test_approx_eq A*B full(A)*full(B)
 end
 
+# check that col/rowstop is ≥ 0
+A = brand(3,4,-2,2)
+@test BandedMatrices.colstop(A, 1) == BandedMatrices.colstop(A, 2) == 0
+@test BandedMatrices.colstop(A, 3) == 1
 
+A = brand(3,4,2,-2)
+@test BandedMatrices.rowstop(A, 1) == BandedMatrices.rowstop(A, 2) == 0
+@test BandedMatrices.rowstop(A, 3) == 1
 
 # test trivial convert routines