Two questions: The first one: Solving an equation:
solve(sin(x)==0,x)
gives the solution [a=pi]
but
solve([sin(x)==0,sin(x)==0],x)
raises to the somehow better solution [[a == pi*z425]] Where is the difference between the two equations?
A second one: A previous version of sage 5.something could solve
solve([sin(x)==0,-sin(x)==0],x)
However Sage 6.4.1 Returns an empty list.
I have now looked at the underlying code for solve. It turns out that if the first argument of solve is an equation or a list of just one equation the object function sage.symbolic.expression.Expression.solve is used. This explains why the output of
solve([sin(x)==0,sin(x)==0],x
and
solve([sin(x)==0],x)
may differ. To force to get all solutions in the first case one can use
solve(sin(x)==0,x,to_poly_solve='force')
Another thing I've found out is that in the definition of the underlying maxima function solve is declared as
solve ([eqn_1, …, eqn_n], [x_1, …, x_n]) so the number of equations should match the number of variables.
If one reformulates the problem to
solve(-sin(x)*sin(x)==0,x,to_poly_solve='force')
all solutions will be displayed.
However I liked the behaviour of previous Versions of sage That is: If solve could't find a solution the original equation was returned. That way it was clear that there may exist solutions sage could not found.
Asked: 2015-02-16 10:03:27 +0100
Seen: 337 times
Last updated: Feb 23 '15
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