subs command is not working on differentiation in MATLAB
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I have defined theta1 and theta2 as my random functions of time. I have defined vec_a1 and vec_v1 by differentiaing them. Afterwards when I am defining theta1 and theta2 and trying to evaluate vec_a1 and vec_v1 it is not converting to numerical values.
g = -9.81;
I1=1;I2=1.5;l1=2;l2=1;rho1=1.1;rho2=0.4;
syms theta1(t) theta2(t)
vec_rho1 = [rho1*cos(theta1), rho1*sin(theta1)];
vec_l1 = [l1*cos(theta1), l1*sin(theta1)];
vec_rho2 = vec_l1 + [rho2*cos(theta2), rho2*sin(theta2)];
vec_l2 = vec_l1 + [l2*cos(theta2), l2*sin(theta2)];
vec_v1 = diff(vec_rho1, t);
vec_a1 = diff(vec_v1, t);
vec_v2 = diff(vec_rho2, t);
vec_a2 = diff(vec_v2, t);
theta1=0.02*t;
theta2=0.3*t;
xx=1
vec_a1=subs(vec_a1)
x=vec_a1(xx);
x=double(x)
댓글 수: 3
Walter Roberson
2022년 6월 5일
subs(expression) is well defined. It means that matlab should look through all of the symvar() and replace them by their values in scope.
답변 (2개)
Dyuman Joshi
2022년 6월 5일
g = -9.81;
I1=1;I2=1.5;l1=2;l2=1;rho1=1.1;rho2=0.4;
syms theta1(t) theta2(t)
theta1=0.02*t;
theta2=0.3*t;
vec_rho1 = [rho1*cos(theta1), rho1*sin(theta1)];
vec_l1 = [l1*cos(theta1), l1*sin(theta1)];
vec_rho2 = vec_l1 + [rho2*cos(theta2), rho2*sin(theta2)];
vec_l2 = vec_l1 + [l2*cos(theta2), l2*sin(theta2)];
vec_v1 = diff(vec_rho1, t);
vec_a1 = diff(vec_v1, t);
vec_v2 = diff(vec_rho2, t);
vec_a2 = diff(vec_v2, t);
xx=1;
x=subs(vec_a1,t,xx)
double(x)
댓글 수: 0
Walter Roberson
2022년 6월 5일
theta1(t)=0.02*t;
theta2(t)=0.3*t;
That is, you had replaced the function theta1 (a function of t) with the symbolic variable theta1 that was not a function.
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