Ranjit a écrit :
> 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
>
The formula.subs_expr (equation) doesn't recognize all sub-product or
all sub-sum, but recognize ONE term in a sum, even a complex one, so I
test with succes the code :
coef = H.coefficient(sigma(r), 2)
H.subs_expr(coef*sigma(r)^2==epsilon*sigma(r)^2)
epsilon*sigma(r)^2 + sqrt(beta)*sqrt(beta_0)*h*sigma(r)/R +
a*beta_0^2*sigma(r)^4/(R^4*beta) + 1/2*D[0](sigma)(r)^2
Do I answer to your question ?
F.
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