update the value of k in the numerator

i want to create a transfer function with num=[k*30] and den=[1 1 6 8] and k=1. But I need to change the value of k and it is automatically updated in the num. How can i do?

Answer 1

[Star Strider]

Create an anonymous function from the tf function call:

Example —

s = tf('s');
h = @(k) tf(k*30, [1 1 6 8]);

for k = 1:3
    sys = h(k)
end

sys =

            30
    -------------------
    s^3 + s^2 + 6 s + 8

Continuous-time transfer function.

sys =

            60
    -------------------
    s^3 + s^2 + 6 s + 8

Continuous-time transfer function.

sys =

            90
    -------------------
    s^3 + s^2 + 6 s + 8

Continuous-time transfer function.

Answer 2

[Walter Roberson]

One way is to construct symbolic transfer functions and manage them yourself, doing the calculations with laplace() and so on.

Alternately see https://www.mathworks.com/matlabcentral/answers/305339-how-to-create-a-transfer-function-with-gain-k#comment_395202