MATLAB Central Newsreader - symbolic partials

symbolic partials

Steve — Fri, 12 Oct 2007 20:08:38 -0400

How do I take a partial derivative of a function with
symbols? For example, when I try
f=x*y
diff(x,'y')
I just get zero. Any suggestions?

Thanks.

Re: symbolic partials

carlos lopez — Fri, 12 Oct 2007 20:17:46 -0400

"Steve " <steveDEL.bachmeierDEL@yahoo.com> wrote in message
<feok86$hqa$1@fred.mathworks.com>...
> How do I take a partial derivative of a function with
> symbols? For example, when I try
> f=x*y
> diff(x,'y')
Maybe you are trying to produce
diff(x,'f')
instead
Regards
Carlos

Re: symbolic partials

Steve — Fri, 12 Oct 2007 20:36:14 -0400

Oops, I meant that diff(f,'x') gives me zero. So,

f=x*y
diff(f,'x')
ans=0

I'm looking for
ans=y

Ideas?

"carlos lopez" <clv2clv_00000000_@adinet.com.uy> wrote in
message <feokpa$4g$1@fred.mathworks.com>...
> "Steve " <steveDEL.bachmeierDEL@yahoo.com> wrote in message
> <feok86$hqa$1@fred.mathworks.com>...
> > How do I take a partial derivative of a function with
> > symbols? For example, when I try
> > f=x*y
> > diff(x,'y')
> Maybe you are trying to produce
> diff(x,'f')
> instead
> Regards
> Carlos
>

Re: symbolic partials

carlos lopez — Thu, 01 Nov 2007 20:47:00 -0400

x = sym('x');
t = sym('t');
f=x*t;
diff(f,'t')
ans =
x
Apparently you did not declare the terms as "sym"
Hope this helps
Carlos