# How do you work out the numerator of a transfer function?

• bick

#### bick

How do you work out the numerator of a transfer function?

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G(s)= 60Ka / s(s+2)(s+6)

what is the numerator you have to use in MATLAB

You'd need the value of Ka. However, remember that this is just a gain term; it has no effect on the location of any poles or zeros that you might have.

If, on the other hand, you're supposed to SOLVE for Ka, they usually tell you what the gain at DC is (i.e. s=0)

EDIT: And welcome to PhysicsForums!

MATLABdude said:
You'd need the value of Ka. However, remember that this is just a gain term; it has no effect on the location of any poles or zeros that you might have.

If, on the other hand, you're supposed to SOLVE for Ka, they usually tell you what the gain at DC is (i.e. s=0)

EDIT: And welcome to PhysicsForums!

Complementing this answer. If you want the root locus, simply use 1 as numerator. After you find the gain that satisfies your specifications, divide it by 60 to obtain Ka.