On 03/21/13 01:54, Jaime Villate wrote:
>
> (%i1) display2d: false$
> (%i2) eq1: x^2*y=1+c*x$
> (%i3) depends(y,x)$
> (%i4) eliminate ([eq1, diff(eq1,x)], [c]);
>
> (%o4) [-x^3*'diff(y,x,1)-x^2*y-1]
>
Thanks, that works very well for most cases.
I cannot seem to get my head around this one. A family of straight
lines at a distance P from the origin. This is not homework, I am
trying to learn maxima and going through an ODE text from 20 years
ago... The text cost $9.95 at Cal. 99.50, now?
I have a solution, but,
kill(all);
display2d:false;
eq1:a*x+b*y+c=0; /* line */
eq2:p^2=c^2/(a^2+b^2); /* distance */
depends(y,x);
eq3:diff(eq1,x);
eq4:apply("+",solve(eq1,c)^2);
eq5:apply("+",solve(eq2,c^2));
eq6:expand(rhs(eq4)/b^2) = expand(rhs(eq5)/b^2);
eq7:apply("+",solve(eq3,'diff(y,x)));
load ("lrats");
eq8:fullratsubst(rhs(eq7)=lhs(eq7),eq6);
eq9:factor(eq8);
It would be nicer if I could formulate it so eliminate(...) works.
Also, I cannot seem to find an easier way than apply("+",...) to get
from a list to an equation I can manipulate.
Tom Dean