--- a/+sbp/+implementations/d4_variable_6.m	Sun Nov 04 12:36:30 2018 -0800
+++ b/+sbp/+implementations/d4_variable_6.m	Wed Nov 21 18:29:29 2018 -0800
@@ -85,7 +85,7 @@
     scheme_radius = (scheme_width-1)/2;
     r = (1+scheme_radius):(m-scheme_radius);
 
-    function D2 = D2_fun(c)
+    function [D2, B] = D2_fun(c)
 
         Mm3 =  c(r-2)/0.40e2 + c(r-1)/0.40e2 - 0.11e2/0.360e3 * c(r-3) - 0.11e2/0.360e3 * c(r);
         Mm2 =  c(r-3)/0.20e2 - 0.3e1/0.10e2 * c(r-1) + c(r+1)/0.20e2 + 0.7e1/0.40e2 * c(r) + 0.7e1/0.40e2 * c(r-2);
@@ -128,6 +128,7 @@
         M=M/h;
 
         D2 = HI*(-M - c(1)*e_l*d1_l' + c(m)*e_r*d1_r');
+        B = HI*M;
     end
     D2 = @D2_fun;