Symbolic Substitution(subs) is not working , why?
조회 수: 7 (최근 30일)
이전 댓글 표시
T(t) =
(25*diff(r1(t), t)^2)/12 + (25*diff(r2(t), t)^2)/8 + (25*cos(r1(t))^2*diff(r1(t), t)^2)/4 + (25*sin(r1(t))^2*diff(r1(t), t)^2)/4 + (3*(5*cos(r1(t))*diff(r1(t), t) + (5*cos(r2(t))*diff(r2(t), t))/2)^2)/2 + (3*(5*sin(r1(t))*diff(r1(t), t) + (5*sin(r2(t))*diff(r2(t), t))/2)^2)/2
T is gained from somewhere which is long story but it works perfectly fine. My code is following:
syms T r1(t) k1
subs(T,r1,k1);
P1=diff(T,k1);
Because I can't differentiate in terms of symbolic function, I wanted to replace r1 with k1, but it doesn't replace and subs function gives back these:
ans(t) =
(25*diff(r2(t), t)^2)/8 + (75*cos(r2(t))^2*diff(r2(t), t)^2)/8 + (75*sin(r2(t))^2*diff(r2(t), t)^2)/8
Somehow r1(t)'s are disappeared but couldn't been replaced with k1. Because there is not k1 in substituted function,differentiation(diff) gives back just 0(zero) which is normal.
Can someone explain me the situation please?
댓글 수: 0
채택된 답변
Walter Roberson
2018년 7월 27일
No, the substitution is working. But you have diff(r1(t),t) and when you replace r1(t) with k1, that becomes diff(k1, t) and since k1 is independent of t, the diff() becomes 0.
댓글 수: 2
Walter Roberson
2018년 8월 1일
But what I recommend is that you look at the first example in odeFunction() to see how to convert equations with derivatives into systems of equations.
추가 답변 (0개)
참고 항목
카테고리
Help Center 및 File Exchange에서 Assumptions에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!