expJ:listarray(J);
(expJ) ["-(l[1]*l[3]*m[3]*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[1](t))+(2*l[1]*l[2]*m[3]+l[1]*l[2]*m[2])*('diff(r[2](t),t,1))^2*sin(r[2](t)-r[1](t))-l[1]*m[1]*g*cos(r[1](t)))/2","-(l[2]*l[3]*m[3]*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[2](t))+((-2*l[1]*l[2]*m[3])-l[1]*l[2]*m[2])*('diff(r[1](t),t,1))^2*sin(r[2](t)-r[1](t))-2*l[2]*m[2]*g*cos(r[2](t)))/2","(l[2]*l[3]*m[3]*('diff(r[2](t),t,1))^2*sin(r[3](t)-r[2](t))+l[1]*l[3]*m[3]*('diff(r[1](t),t,1))^2*sin(r[3](t)-r[1](t))+3*l[3]*m[3]*g*cos(r[3](t)))/2"]
for i:1 thru 3 do(
for k:1 thru 3 do(
J[i,1]:ssubst("m3","m[3]",J[i,1])
));
我想用算法替换m前面的数字,因为它们分别是1,2,3,但是当我放mi时,它会将其识别为不同的变量,因此我需要以某种方式指示ssubs(“ mi”,“ m [ i]“,J [i,1]),因为i与m分开。 有什么建议吗?
答案 0 :(得分:0)
好的,这是用v(k)
代替v[k]
的一种方法。我相信这是可以的,因为Matlab可以识别数组下标的括号。
%o5是您在上面提供的输入(作为字符串)。我已经在%o7中解析了字符串,并在%o10中提取了下标变量的列表(通过sublist
和subvarp
)。从那里,我在%o14中创建了一个列表v(k) = v[k]
,然后将它们替换回%o15中的已解析表达式中。
我希望这将对您有所帮助。您可能仍需要修改此方法才能获得所需的内容,但是无论如何,我都会重申我对字符串处理的强烈建议。如果还有更多事情要做,那么可以肯定的是,使用表达式比使用字符串来实现更好。
(%o5) [-(l[1]*l[3]*m[3]*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[1](t))+(2*l[1]*l[\
2]*m[3]+l[1]*l[2]*m[2])*('diff(r[2](t),t,1))^2*sin(r[2](t)-r[1](t))-l[1]*m[1]*\
g*cos(r[1](t)))/2, -(l[2]*l[3]*m[3]*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[2](t)\
)+((-2*l[1]*l[2]*m[3])-l[1]*l[2]*m[2])*('diff(r[1](t),t,1))^2*sin(r[2](t)-r[1]\
(t))-2*l[2]*m[2]*g*cos(r[2](t)))/2, (l[2]*l[3]*m[3]*('diff(r[2](t),t,1))^2*sin\
(r[3](t)-r[2](t))+l[1]*l[3]*m[3]*('diff(r[1](t),t,1))^2*sin(r[3](t)-r[1](t))+3\
*l[3]*m[3]*g*cos(r[3](t)))/2]
(%i6) linel:65;
(%o6) 65
(%i7) map (parse_string, %o5);
d 2
(%o7) [((- l l m (-- (r (t))) sin(r (t) - r (t)))
1 3 3 dt 3 3 1
d 2
- (2 l l m + l l m ) (-- (r (t))) sin(r (t) - r (t))
1 2 3 1 2 2 dt 2 2 1
d 2
+ l m g cos(r (t)))/2, ((- l l m (-- (r (t)))
1 1 1 2 3 3 dt 3
d 2
sin(r (t) - r (t))) - ((- 2 l l m ) - l l m ) (-- (r (t)))
3 2 1 2 3 1 2 2 dt 1
sin(r (t) - r (t)) + 2 l m g cos(r (t)))/2,
2 1 2 2 2
d 2
(l l m (-- (r (t))) sin(r (t) - r (t))
2 3 3 dt 2 3 2
d 2
+ l l m (-- (r (t))) sin(r (t) - r (t))
1 3 3 dt 1 3 1
+ 3 l m g cos(r (t)))/2]
3 3 3
(%i8) grind (%);
[((-l[1]*l[3]*m[3]*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[1](t)))
-(2*l[1]*l[2]*m[3]+l[1]*l[2]*m[2])
*('diff(r[2](t),t,1))^2*sin(r[2](t)-r[1](t))
+l[1]*m[1]*g*cos(r[1](t)))
/2,
((-l[2]*l[3]*m[3]*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[2](t)))
-((-2*l[1]*l[2]*m[3])-l[1]*l[2]*m[2])
*('diff(r[1](t),t,1))^2*sin(r[2](t)-r[1](t))
+2*l[2]*m[2]*g*cos(r[2](t)))
/2,
(l[2]*l[3]*m[3]*('diff(r[2](t),t,1))^2*sin(r[3](t)-r[2](t))
+l[1]*l[3]*m[3]*('diff(r[1](t),t,1))^2*sin(r[3](t)-r[1](t))
+3*l[3]*m[3]*g*cos(r[3](t)))
/2]$
(%o8) done
(%i9) listofvars (%o7);
(%o9) [l , m , g, t, l , m , m , l ]
1 1 2 2 3 3
(%i10) sublist (%, subvarp);
(%o10) [l , m , l , m , m , l ]
1 1 2 2 3 3
(%i11) map (op, %o10);
(%o11) [l, m, l, m, m, l]
(%i12) map (args, %o10);
(%o12) [[1], [1], [2], [2], [3], [3]]
(%i13) map (lambda ([v], apply (op(v), args(v))), %o10);
(%o13) [l(1), m(1), l(2), m(2), m(3), l(3)]
(%i14) map (lambda ([v1, v2], v1=v2), %o10, %o13);
(%o14) [l = l(1), m = m(1), l = l(2), m = m(2), m = m(3),
1 1 2 2 3
l = l(3)]
3
(%i15) subst (%, %o7);
d 2
(%o15) [((- l(1) l(3) m(3) (-- (r (t))) sin(r (t) - r (t)))
dt 3 3 1
d 2
- (2 l(1) l(2) m(3) + l(1) l(2) m(2)) (-- (r (t)))
dt 2
sin(r (t) - r (t)) + l(1) m(1) g cos(r (t)))/2,
2 1 1
d 2
((- l(2) l(3) m(3) (-- (r (t))) sin(r (t) - r (t)))
dt 3 3 2
d 2
- ((- 2 l(1) l(2) m(3)) - l(1) l(2) m(2)) (-- (r (t)))
dt 1
sin(r (t) - r (t)) + 2 l(2) m(2) g cos(r (t)))/2,
2 1 2
d 2
(l(2) l(3) m(3) (-- (r (t))) sin(r (t) - r (t))
dt 2 3 2
d 2
+ l(1) l(3) m(3) (-- (r (t))) sin(r (t) - r (t))
dt 1 3 1
+ 3 l(3) m(3) g cos(r (t)))/2]
3
(%i16) grind (%);
[((-l(1)*l(3)*m(3)*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[1](t)))
-(2*l(1)*l(2)*m(3)+l(1)*l(2)*m(2))
*('diff(r[2](t),t,1))^2*sin(r[2](t)-r[1](t))
+l(1)*m(1)*g*cos(r[1](t)))
/2,
((-l(2)*l(3)*m(3)*('diff(r[3](t),t,1))^2*sin(r[3](t)-r[2](t)))
-((-2*l(1)*l(2)*m(3))-l(1)*l(2)*m(2))
*('diff(r[1](t),t,1))^2*sin(r[2](t)-r[1](t))
+2*l(2)*m(2)*g*cos(r[2](t)))
/2,
(l(2)*l(3)*m(3)*('diff(r[2](t),t,1))^2*sin(r[3](t)-r[2](t))
+l(1)*l(3)*m(3)*('diff(r[1](t),t,1))^2*sin(r[3](t)-r[1](t))
+3*l(3)*m(3)*g*cos(r[3](t)))
/2]$
(%o16) done
(%i17) listofvars (%o15);
(%o17) [g, t]