Add a method decompress_single_color!

Author: amontoison

src/decompression.jl

@@ -537,6 +537,59 @@ function decompress!(
     return A
 end
 
+function decompress_single_color!(
+    A::SparseMatrixCSC,
+    b::AbstractVector,
+    c::Integer,
+    result::StarSetColoringResult,
+    uplo::Symbol=:F,
+)
+    (; ag, compressed_indices, group) = result
+    (; S) = ag
+    if (result.decompression_uplo == :F) && (result.decompression_uplo != uplo)
+        lower_index = (c - 1) * S.n + 1
+        upper_index = c * S.n
+        rvS = rowvals(S)
+        for j in group[c]
+            for k in nzrange(S, j)
+                # Check if the color c is used to recover A[i,j] / A[j,i]
+                if lower_index <= compressed_indices[k] <= upper_index
+                    i = rvS[k]
+                    if i == j
+                        # Recover the diagonal coefficients of A
+                        A[i, i] = b[i]
+                    else
+                        # Recover the off-diagonal coefficients of A
+                        if in_triangle(i, j, uplo)
+                            A[i, j] = b[i]
+                        end
+                        if in_triangle(j, i, uplo)
+                            A[j, i] = b[i]
+                        end
+                    end
+                end
+            end
+        end
+    else
+        @assert result.decompression_uplo == uplo
+        uplo == :F && check_same_pattern(A, S)
+        lower_index = (c - 1) * S.n + 1
+        upper_index = c * S.n
+        rvA = rowvals(A)
+        nzA = nonzeros(A)
+        for j in group[c]
+            for k in nzrange(A, j)
+                # Check if the color c is used to recover A[i,j]
+                if lower_index <= compressed_indices[k] <= upper_index
+                    i = rvA[k]
+                    nzA[k] = b[i]
+                end
+            end
+        end
+    end
+    return A
+end
+
 ## TreeSetColoringResult
 
 function decompress!(