yy=sin(x)+0.2*sin(2x)-0.3*sin(3x);
MATLAB has absolutely no implied multiplication anywhere. Not even in the symbolic toolbox. 2x is not a valid expression in MATLAB.
The only cases in which a number can be directly followed by a letter in MATLAB are:
- in the middle of an identifier (which would have to start with a letter, not a number or underscore)
- in a single-quoted character vector or double-quoted string object
- in a comment
- A number may be directly followed by i or j to indicate multiplication by sqrt(-1), such as 5i meaning 5*sqrt(-1). i and j are case-sensitive for this purpose
- A number may be directly followed by e or E or d or D provided that is followed by an optional + or - that is then followed by an integer; this indicates an exponent. For example 5.2e3
- A 0 at the beginning of a number may be immediately followed by a b that is then followed by a series of 0 and 1 to indicate binary numbers. The sequence of binary numbers may be followed by s or u and then the integer 8, 16, 32, or 64
- A 0 at the beginning of a number may be immediately followed by a x that is then followed by a series of hex digits 0 to 9, A-F or a-f, to indicate hexadecimal numbers. The sequence of hexadecimal numbers may be followed by s or u and then the integer 8, 16, 32, or 64
In all other cases, you need an operator between the number and the letter, such as 2*x intead of 2x.
