There is a comma separated list containing four variables, the variables a, b, c, and d. Every time you write a list of variables separated by commas then you are writing a comma separated list. Most commonly you would write a comma separated list when calling a function or operator:
It is important to note that a comma separated list is not one variable! Sometimes we want to create a comma separated list from one variable: MATLAB has two ways of doing this, these are from a cell array:
But both of these are still exactly equivalent to what I wrote at the top: they will generate this:
and remember NOT ONE VARIABLE. Therefore the syntax you used:
is an error because
creates a comma-separated list, exactly equivalent to this:
and it is ambiguous what role the .C should have on the end.
is exactly equivalent to writing this list of independent variables:
and yet would you expect to write this list of independent variables:
and expect it to get the C field of X, Y, and Z?