I want to ask how to define the partial fraction code single number located at the numerator?

>> syms s

>> F=4(3*s+13)/(8*s^2+s+4)

F=4(3*s+13)/(8*s^2+s+4)

↑

Invalid expression. When calling a function or indexing a variable, use parentheses.

Otherwise, check for mismatched delimiters.

Answer 1

[Arif Hoq]

use multiplication operator (*) before parentheses

syms s
F=4*(3*s+13)/(8*s^2+s+4)

F = 

Answer 2

[John D'Errico]

Remember that MATLAB does not understand implicit multiplication. That is, 4x is not interpreted as 4*x. In MATLAB, 4x is just a syntax error. (With the subtle and singular exception that things like 1i are interpreted by the parser as 1*sqrt(-1).)

What did MATLAB tell you? That MATLAB had a problem where the little arrow points. And you already knew to use 8*s^2, to form that product in another place, so you do apparently understand the need for an * operator.

This works of course:

syms s
F=4*(3*s+13)/(8*s^2+s+4)

F = 

Error messages usually try to point out where a problem lies. In this case, MATLAB was confused. It saw this:

4(3*s+13)

and said, ok, 4 must be a function, and 3*s+13 is the argument to that function. Wait, a number cannot be the name of a function. So then 4 must be a variable, since parens are also used to index into a variable. But then 4 is not the name of a variable either. As that point, MATLAB just gave up and threw an error.

Computers are easily confused.