Thank you for your answer. And what should be done in this case? On Sunday, May 3, 2015 at 10:27:44 AM UTC+3, Dominique Laurain wrote: > > > I bet I know why : we can trick mathematical sofware in various > ways,...,but why should we ? > find_root is "numerical" function to get approximate real root of function > in interval....when we know ( "theorically") the root exists !! > the function can be implemented in various ways, and for example, if using > a Newton tangent algorithm, it needs only the function to be continuous and > with derivative, to get, in finite steps, a better approximate as the one > given > > In > http://www.sagemath.org/doc/reference/numerical/sage/numerical/optimize.html > the help doc gives xtol=1.e-12 (default) and the algorithm terminated when > new approximate x_n is in range [pi/2 - xtol, pi/2 + xtol] for your function > For me, "find_root_approximate" would have been better name than find_root > > On Sunday, 3 May 2015 00:50:55 UTC+2, Paul Royik wrote: >> >> Don't know why but find_root(x*tan(x), -1, 5) gives me 1.570796 which is >> incorrect, since it is pi/2, the value at which tangent doesn't exist. >> >
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