kcrisman wrote:
On Wednesday, June 12, 2013 8:09:02 PM UTC-4, leif wrote:robin hankin wrote: > hello, sage 5.9 > > If solve() gives an unspecificed integer, how do I substitute a > particular value into the expression? > > subs() does not work as expected/desired because the free variables > don't seem to be defined. > > sage: a=solve(sin(x)==0,x,to_poly_solve='force');a > [x == 2*pi*z38, x == pi + 2*pi*z36] > sage: a[0].rhs() > 2*pi*z38 > sage: a[0].rhs().subs(z38,3) > --------------------------------------------------------------------------- > NameError Traceback (most recent call last) > <ipython-input-3-1ded925632b3> in <module>() > ----> 1 a[Integer(0)].rhs().subs(z38,Integer(3)) > > NameError: name 'z38' is not defined > sage: Smells like a bug... Not exactly. The documentation for solve makes it clear (I hope!) in the examples that these are "generic" variables generated by Maxima which we do not make "Sage" variables. They just mean, "any old integer" (hence 'z'). That said, it would be useful to allow them to be used in this way. The problem is that a user might already have defined z38 to mean something else...
Well, in the latter case, Sage should be able to automatically rename them to avoid name clashes... ;-)
Or at least .subs() should also work with ('z36',3), say, i.e., strings representing variable names, or dictionaries mapping these to expressions (or concrete values, probably with typechecking...).
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