USER_PROBLEM: Fix plane selection for magnetic flux integration.

Signed-off-by: Grzegorz Kowal <grzegorz@amuncode.org>

problems/flux-tubes.in

@@ -0,0 +1,64 @@
+# problem name and parameters
+#
+problem              = "flux-tubes"
+profile              = "sincos"
+beta                 = 2.00d+00
+bgui                 = 0.00d+00
+delta                = 3.16d-03
+
+# diffusion coefficients
+#
+viscosity            = 1.00d-05
+resistivity          = 1.00d-05
+glm_source_terms     = "none"
+
+# random number generator
+#
+gentype              = "same"
+
+# physics
+#
+equation_system      = "mhd"
+equation_of_state    = "iso"
+
+# methods
+#
+time_advance         = "ssprk3(2)4"
+riemann_solver       = "roe"
+reconstruction       = "ocmp5"
+
+# mesh parameters
+#
+xmin                 = -5.00d-01
+xmax                 =  5.00d-01
+ymin                 = -5.00d-01
+ymax                 =  5.00d-01
+
+# refinement control
+#
+ncells               = 32
+minlev               = 1
+maxlev               = 9
+refinement_variables = "vort jabs"
+currmin              = 5.0d-02
+currmax              = 2.0d-01
+vortmin              = 5.0d-02
+vortmax              = 2.0d-01
+
+# boundary conditions
+#
+xlbndry              = "user"
+xubndry              = "user"
+ylbndry              = "user"
+yubndry              = "user"
+
+# runtime control parameters
+#
+tmax                 = 2.0d+00
+cfl                  = 5.0d-01
+
+# data output control
+#
+snapshot_interval    = 1.0d-01
+compression_format   = "zstd"
+compression_level    = 19