On 6/21/10, Jeffrey Hankins <jhankin1 at gmail.com> wrote:
> Hey...if anyone reads this, do they know how to contact whoever's developing
> the ezunits package? There's something that I want to do in it, but I don't
> think I'm able to.
Well, that would be me. What are you trying to do?
> Also, I don't know what format the implicit_derivative
> routine in the impdiff package is expecting. A demo or an example would have
> helped. At least it is easy to get around the need for it because the
> formula is so simple.
Sorry, I don't know anything about impdiff.
best
Robert Dodier
For implicit differention I define
(%i1) impdiff(eq,y,x,k):=block([y1],
depends(y,x),
diff(eq,x,1),
solve(%%,diff(y,x,1)),
y1:rhs(first(%%)),
hdiff(f,x):=block(diff(f,x),subst(diff(y,x,1)=y1,%%),factor(%%)),
if k=1 then y1
else hdiff(impdiff(eq,y,x,k-1),x))$
Mixed derivatives not supported.
Examples:
(%i2) for k thru 5 do
print(impdiff(u^2+v^2=1,u,v,k));
(%i3) for k thru 5 do
print(impdiff(atan(y/x)=1/2*log(x^2+y^2),y,x,k));
(%i4) for k thru 5 do
print(impdiff(atan(y/x)=1/2*log(x^2+y^2),x,y,k));
For testing Maple code:
>for k to 5 do
> implicitdiff(u^2+v^2=1,u,v$k):
> print(factor(%)); end do:
>for k to 5 do
> implicitdiff(arctan(y/x)=1/2*ln(x^2+y^2),y,x$k):
> print(factor(%)); end do:
> for k to 5 do
> implicitdiff(arctan(y/x)=1/2*ln(x^2+y^2),x,y$k):
> print(factor(%)); end do:
Aleksas Domarkas