>From the formula provided in wikipedia one can switch (by rewrite(cos,sin)) to the formula that uses only cos or sin. It is inefficient, however for general use I would prefer this, because the other direction (from only cos or sin to an expression in which the total order is the same) is not possible.
Maybe we should also add the chebishev_expand helper function (exposed to the users) to the trigonometry module. A bug related to this discussion (if the user wants to switch from the provided formula to another formula): In [15]: cos(x).rewrite(sin) Out[15]: cos(x) This happens because cos._eval_rewrite_as_sin returns sin(x+pi/2) which autosimplifies(as it should) to cos(x). I suppose that it should return sqrt(1-sin(x)**2) -- You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
