Add missing forward declaration in slepc_spectral_transformation.h

Co-authored-by: Alex Kokomov <KokomovAlex@gmail.com>

diff --git a/include/deal.II/lac/slepc_spectral_transformation.h b/include/deal.II/lac/slepc_spectral_transformation.h
index 12ed606d84b986d5183a98baa7fee5bfcf3ffaca..da6a94767d0b82e00b9849f7d29c628dd31d562d 100644 (file)
--- a/include/deal.II/lac/slepc_spectral_transformation.h
+++ b/include/deal.II/lac/slepc_spectral_transformation.h
@@ -44,6 +44,9 @@ namespace PETScWrappers
 
 namespace SLEPcWrappers
 {
+  // forward declaration
+  class SolverBase;
+
   /**
    * Base class for spectral transformation classes using the SLEPc solvers
    * which are selected based on flags passed to the spectral transformation.