example of 3d function field

benchmarks/3d/function_field.geo

+
+lc = 0.5;
+Point(1) = {0, 0, 0, lc};
+Point(2) = {1, 0,  0, lc} ;
+Point(3) = {1, 1, 0, lc} ;
+Point(4) = {0, 1, 0, lc} ;
+Line(1) = {1,2} ;
+Line(2) = {3,2} ;
+Line(3) = {3,4} ;
+Line(4) = {4,1} ;
+Line Loop(5) = {4,1,-2,3} ;
+Plane Surface(6) = {5} ;
+Extrude {0,0,1} { Surface{6}; }
+
+Function Field(1) = "Cos(2*3.14*x)/5 + 0.21";
+Characteristic Length Field{1};