I'm trying to figure out how to do a simple substitution. I've the
following code:
var('r beta beta_0 R a h')
psi=function('psi',r)
sigma=function('sigma',r)
H_0=function('H_0',r)
H_grad = lambda psi : (1/2)*(beta/beta_0)*R^2*(psi.diff(r))^2
H_0(psi) = -(1/2)*(beta/beta_0-1)*psi^2 + beta*a*psi^4 + beta*h*psi
H_1=H_grad((1/R)*(beta_0/beta)^(1/2)*sigma)
H=H_1+H_0((1/R)*(beta_0/beta)^(1/2)*sigma)
H=H.simplify_radical().expand().collect(sigma^2)
H
Let's say I want to rewrite the coefficient on sigma^2 as simply
epsilon, how can I do that?
When I try a simpler example, it's straightforward but the same thing
doesn't seem to work on the expression above:
var('a b c')
f(x)=(a+b)*x^2
f.subs(a+b==c)
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