how to substitute known values
- Subject: how to substitute known values
- From: Barton Willis
- Date: Wed, 6 Apr 2011 07:56:09 -0500
-----Leo Butler <l.butler at ed.ac.uk> wrote: -----
>?I?think?the?function?you?want?is?psubst.
>
>?psubst([x=3,?y=4,?diff(x,t)?=?5,?diff(y,t)=7],?diff(sqrt(x^2+y^2),t));
>
>?should?do?what?you?want.
No, isn't the cure:
(%i1) depends(x,t,y,t);
(%o1) [x(t),y(t)]
(%i2) psubst([x=3, y=4, diff(x,t) = 5, diff(y,t)=7], diff(sqrt(x^2+y^2),t));
(%o2) 0
(%i3) psubst([diff(x,t) = 5, diff(y,t)=7,x=3, y=4], diff(sqrt(x^2+y^2),t));
(%o3) 43/5
--Barton