Thank you very much Francois, much more explicit than I expected!!! On Jan 23, 4:39 pm, Francois Maltey <fmal...@nerim.fr> wrote: > Dox a crit : > > > Hi guys! I have an easy question... got an expression with > > exponentials, say exp(x)+exp(-x), How can I get the result in terms of > > hyperbolic functions > > 1/ First you can use the expr.subs method : > > y=exp(x)+exp(-x) > y.subs(exp(x)==sinh(x)+cosh(x)).subs(exp(-x)=cosh(x)-sinh(x)) > > [You must call subs for all subexpressions : exp(x) and (exp(-x)] > > 2/ Second you can also play with match, find and subs : > > w0=SR.wild(0) # w0 is now a matching subexpression > y.subs(exp(w0)==cosh(w0)+sinh(w0)) > > The result is sinh(-x) + sinh(x) + cosh(-x) + cosh(x) > And then y.subs(exp(w0)==cosh(w0)+sinh(w0)).simplify() is pretty. > > I think it's impossible to subs the function exp to the other (sum of) > function(s) exp=cosh+sinh. > You must use the regular subexpression SR.wild(0) [look at help about > find, subs and match] > > 3/ Third, you can use the outside Sage function rewrite published > athttp://wiki.sagemath.org/symbolics/rewriteand get the attachement file > rewriteXXXX.sage, load it. > and call rewrite (y, rules="exp2sinhcosh"). > > Choice what you prefer ! > > F.
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