Add tests to increase coverage of matrix inversion

Author: mfasi

test/code_gen_test.jl

@@ -71,8 +71,9 @@ using LinearAlgebra, StaticArrays
     for i = 1:4 #Not high-precision test for Matlab and C
         (graph, crefs) = graph_ps_degopt([3 4 2 a[i] 1 0])
         add_ldiv!(graph, :R1, :B4, graph.outputs[1])
+        add_ldiv!(graph, :R1inv, :R1, :I)
         add_lincomb!(graph,:Q, [1, 2, 3], [:I, :I, :I])
-        add_lincomb!(graph,:R0, [2, 3, 4], [:I, :Q, :R1])
+        add_lincomb!(graph,:R0, [2, 3, 4, 5], [:I, :Q, :R1, :R1inv])
         clear_outputs!(graph)
         add_output!(graph, :R0)