Extract num and den in symbolic expression.
조회 수: 19 (최근 30일)
이전 댓글 표시
The 'tf' function in Control Systems needs numerator and denometer in a vector of decreasing powers of s.
For example a numerator of a*s^2 + b*s + c needs to be num= [a b c];. I have been cutting and pasting the necessary coefficients
but to do this I have to pause my program. Is there a way to extract the appropriate vector(s) programatically?
Thanks,
Bruce Taylor
댓글 수: 0
채택된 답변
Star Strider
2019년 7월 24일
댓글 수: 3
Star Strider
2019년 7월 24일
I thought you had already isolated the numerator and denominator.
Try this:
syms a b c d e f g s
sys=(a*s^2+b*s+c)/(d*s^3+e*s^2+f*s+g)
sys = subs(sys,{a,b,c,d,e,f,g},{3,6,8,1,2,9,5})
[np,dp] = numden(sys)
n = sym2poly(np)
d = sym2poly(dp)
producing:
sys =
(a*s^2 + b*s + c)/(d*s^3 + e*s^2 + f*s + g)
sys =
(3*s^2 + 6*s + 8)/(s^3 + 2*s^2 + 9*s + 5)
np =
3*s^2 + 6*s + 8
dp =
s^3 + 2*s^2 + 9*s + 5
n =
3 6 8
d =
1 2 9 5
Note that this will only work with numeric coefficients. It will error with symbolic coefficients.
Walter Roberson
2019년 7월 25일
Star Strider is correct, MATLAB transfer functions, tf() and ss(), cannot support symbolic expressions.
추가 답변 (1개)
참고 항목
카테고리
Help Center 및 File Exchange에서 Symbolic Math Toolbox에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!