#9824: improve desolve_system initial condition documentation
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Reporter: rhinton | Owner: burcin
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.7
Component: calculus | Keywords: calculus, maxima, symbolics
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Old description:
> desolve_system apparently ignores initial conditions. Notice the
> identical results in the two calls in the following example.
>
> {{{
> sage: t = var('t')
> sage: epsilon = var('epsilon')
> sage: x1 = function('x1', t)
> sage: x2 = function('x2', t)
> sage: de1 = diff(x1,t) == epsilon
> sage: de2 = diff(x2,t) == -2
> sage: desolve_system([de1, de2], [x1, x2], ivar=t)
> [x1(t) == epsilon*t + x1(0), x2(t) == -2*t + x2(0)]
> sage: desolve_system([de1, de2], [x1, x2], ics=[1,1], ivar=t)
> [x1(t) == epsilon*t + x1(0), x2(t) == -2*t + x2(0)]
> }}}
New description:
Edit: See comments for the actual issue.
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desolve_system apparently ignores initial conditions. Notice the
identical results in the two calls in the following example.
{{{
sage: t = var('t')
sage: epsilon = var('epsilon')
sage: x1 = function('x1', t)
sage: x2 = function('x2', t)
sage: de1 = diff(x1,t) == epsilon
sage: de2 = diff(x2,t) == -2
sage: desolve_system([de1, de2], [x1, x2], ivar=t)
[x1(t) == epsilon*t + x1(0), x2(t) == -2*t + x2(0)]
sage: desolve_system([de1, de2], [x1, x2], ics=[1,1], ivar=t)
[x1(t) == epsilon*t + x1(0), x2(t) == -2*t + x2(0)]
}}}
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Comment(by kcrisman):
I agree that we should be explicit here. There is no obvious default for
a diffeq; initial condition of zero is not the same as starting to count
at 0 or 1. Yes, updating the documentation would be great for this.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9824#comment:3>
Sage <http://www.sagemath.org>
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