On 7/24/10 4:38 AM, Renato wrote:
Hi, this seems very basic, but I wasn't able to figure it out. Let's say
I have a function:
sage: f(t)
-4*(5*sqrt(2)*cos(1/2*sqrt(2)*sqrt(5)) -
2*sqrt(5)*sin(1/2*sqrt(2)*sqrt(5)))*sin(1/2*sqrt(5)*t)/(sqrt(5)*sin(1/2*sqrt(2)*sqrt(5))^2
+ sqrt(5)*cos(1/2*sqrt(2)*sqrt(5))^2) +
4*(5*sqrt(2)*sin(1/2*sqrt(2)*sqrt(5)) +
2*sqrt(5)*cos(1/2*sqrt(2)*sqrt(5)))*cos(1/2*sqrt(5)*t)/(sqrt(5)*sin(1/2*sqrt(2)*sqrt(5))^2
+ sqrt(5)*cos(1/2*sqrt(2)*sqrt(5))^2) - 8
how do I tell sage to evaluate numerically everything but sin(), cos()
and t? I.e. I know this function is in the form
f(t) = a*sin(b*t) + c*cos(d*t)
can I tell sage to put it in this form, evaluating numerically a,b,c
and d?
kind regards
renato
It looks like there is also a -8 at the end:
sage: f(t)=-4*(5*sqrt(2)*cos(1/2*sqrt(2)*sqrt(5))
-2*sqrt(5)*sin(1/2*sqrt(2)*sqrt(5)))*sin(1/2*sqrt(5)*t)/(sqrt(5)*sin(1/2*sqrt(2)*sqrt(5))^2+
sqrt(5)*cos(1/2*sqrt(2)*sqrt(5))^2)
+4*(5*sqrt(2)*sin(1/2*sqrt(2)*sqrt(5))
+2*sqrt(5)*cos(1/2*sqrt(2)*sqrt(5)))*cos(1/2*sqrt(5)*t)/(sqrt(5)*sin(1/2*sqrt(2)*sqrt(5))^2+
sqrt(5)*cos(1/2*sqrt(2)*sqrt(5))^2) - 8
sage: f.subs_expr(sqrt(5)==sqrt(5).n(),sqrt(2)==sqrt(2).n())
t |--> 8.13039327042996*sin(1.11803398874989*t) +
12.5656955743861*cos(1.11803398874989*t) - 8
Basically, I used subs_expr to subsititute in numeric values for the
square roots.
Question to the community at large:
It seems like f.n() should do the above (evaluate what it can
numerically, leave the variables alone). But this doesn't work:
sage: f.n()
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
/Users/grout/<ipython console> in <module>()
/Users/grout/sage/local/lib/python2.6/site-packages/sage/symbolic/expression.so
in sage.symbolic.expression.Expression.n
(sage/symbolic/expression.cpp:17042)()
TypeError: cannot evaluate symbolic expression numerically
Thanks,
Jason
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