Mix together flour and sugar well and set aside in large bowl.
In saucepan combine butter, shortening, cocoa and water and bring to boil. Pour over flour and sugar mixture, stirring well.
Add buttermilk with soda mixed into it, eggs, cinnamon and vanilla into bowl with the other ingredients and stir well. Pour into greased 9 x 13 pan and bake 25 minutes at 400 degrees.
Remove cake from oven when done and in saucepan melt butter and combine cocoa and milk. Stir in vanilla and powdered sugar and pecans and stir until desired consistency, adding more powdered sugar if needed and pour over cake while still warm.