I am wondering, if it is somehow possible to directly change a global variable inside a program block like a call-by-reference function call.
Right now this is my work around:
1. The global variable is assigned to a local variable with same name.
2. The local variable is changed as desired
3. In the end the local variable is returned and assigned again to the global variable.
However as I am working with large matrices (sometimes even matrices containing matrices) I would expect a faster running program, if I got rid of the copying forth and back.