[Numpy-discussion] double-precision sqrt?

Adam Ginsburg adam.ginsburg@colorado....
Sat Oct 17 13:08:18 CDT 2009


Hi folks,
   I'm trying to write a ray-tracing code for which high precision is
required.  I also "need" to use square roots.  However, math.sqrt and
numpy.sqrt seem to only use single-precision floats.  Is there a
simple way to make sqrt use higher precision?  Alternately, am I
simply being obtuse?

Thanks,
Adam

Example code:
from scipy.optimize.minpack import fsolve
from numpy import sqrt

sqrt(float64(1.034324523462345))
# 1.0170174646791199
f=lambda x: x**2-float64(1.034324523462345)**2

f(sqrt(float64(1.034324523462345)))
# -0.03550269637326231

fsolve(f,1.01)
# 1.0343245234623459

f(fsolve(f,1.01))
# 1.7763568394002505e-15

fsolve(f,1.01) - sqrt(float64(1.034324523462345))
# 0.017307058783226026


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