Hi
equ0 = term_0 == term_1 + term_2 + term_3
I want to extract term_1 + term_2 to work with.
I have been looking for a long time without success, I read the whole page: link text
example: |p(ρϵe(iθϵ)+w)|2=ρ0ρmϵρme(imθϵ−iθ0+iθm)+ρ0ρmϵρme(−imθϵ+iθ0−iθm)+ρ2mϵρ2m+ρ20
var('term_0 term_1 term_2 term_3')
equ0 = term_0 == term_1 + term_2 + term_3
# use the operands method of expressions
print equ0.rhs().operands()
# subtract third term (the last in the list of operands)
print equ0.rhs() - equ0.rhs().operands()[-1]
# or build expression from list of operands
print sum(equ0.rhs().operands()[:2])Thanks too ndomes.
moreover operands() appears in the link I put above, but I did not see it ;-(, really sorry.
You should really give explicit example with Sage code, so that we really understand what do you want to achieve. Let me take my own example:
sage: equ0 = cos(x) == 3*x^2 + log(x) + 42*sin(x)
sage: equ0
cos(x) == 3*x^2 + log(x) + 42*sin(x)You can first extract the right-hand-side of the equation as follows:
sage: equ0.rhs()
3*x^2 + log(x) + 42*sin(x)Then, you can check that it is an addition:
sage: equ0.rhs().operator()
<function add_vararg at 0x7f5a30600050>For which you can get the operands:
sage: equ0.rhs().operands()
[3*x^2, log(x), 42*sin(x)]You can extract the first two terms of this list:
sage: equ0.rhs().operands()[:2]
[3*x^2, log(x)]You can them add them together:
sage: sum(equ0.rhs().operands()[:2])
3*x^2 + log(x)WARNING the order of the operands is not necessrilly the one you entered:
sage: equ0 = cos(x) == log(x) + 3*x^2 + 42*sin(x)
sage: equ0
cos(x) == 3*x^2 + log(x) + 42*sin(x)Thanks tmonteil, it is exactly what I would like to do ! you said "WARNING the order of the operands is not necessarily the one you entered"
Yes,but if it is the first term I see when I do a show(equ0.rhs()) I suppose it will have the first indice for operands().
Correct, the way symbolic operands are reordered by Sage is deterministic.
Asked: 7 years ago
Seen: 725 times
Last updated: Sep 03 '17
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