Simple symbolic query



Hi

I'm a novice to Maxima and would like some simple advice on how to 
re-arrange the following symbolic Jacobian calculation where x and y are 
ith data points and a and b are variables.

jacobian([y-a*cos(b*x)-b*sin(a*x)],[a,b]);

It can be represented as:

vars:[a,b];
funct:[y-a*cos(b*x)-b*sin(a*x)];
jacobian(funct,vars);

But i would like it more in the form:

vars:[a,b]
f=a*cos(b*x)+b*sin(a*x)
d=y-f
jacobian(d,vars)

which does not work!

Any simple tips please?

Dave Brant