See https://gitlab.onelab.info/gmsh/gmsh/-/issues/2486

--- tutorials/t10.geo.orig	2022-10-27 11:08:31
+++ tutorials/t10.geo	2023-05-23 06:45:47
@@ -52,7 +52,7 @@
 // Say we want to modulate the mesh element sizes using a mathematical function
 // of the spatial coordinates. We can do this with the MathEval field:
 Field[3] = MathEval;
-Field[3].F = "Cos(4*3.14*x) * Sin(4*3.14*y) / 10 + 0.101";
+Field[3].F = "cos(4*3.14*x) * sin(4*3.14*y) / 10 + 0.101";
 
 // We could also combine MathEval with values coming from other fields. For
 // example, let's define a `Distance' field around point 1
--- tutorials/c++/t10.cpp.orig	2022-10-27 11:08:31
+++ tutorials/c++/t10.cpp	2023-05-23 06:53:18
@@ -72,7 +72,7 @@
   // field:
   gmsh::model::mesh::field::add("MathEval", 3);
   gmsh::model::mesh::field::setString(
-    3, "F", "Cos(4*3.14*x) * Sin(4*3.14*y) / 10 + 0.101");
+    3, "F", "cos(4*3.14*x) * sin(4*3.14*y) / 10 + 0.101");
 
   // We could also combine MathEval with values coming from other fields. For
   // example, let's define a `Distance' field around point 1