psi1¶
Evaluates the second derivative of the log gamma function.
Synopsis¶
psi1 (x)
Required Arguments¶
- float
x
(Input) - Argument at which the function is to be evaluated.
Return Value¶
The value of the second derivative of the log gamma function at x
. NaN
is returned if an error occurs.
Description¶
The psi1
function, also called the trigamma function, is defined to be
\[\psi_1(x) = \frac{d^2}{dx^2} \ln \mathit{\Gamma}(x)\]
See gamma for the definition of Γ(x).
The argument x
must not be exactly zero or a negative integer, or
\(\psi_1(x)\) is undefined. Also, x
must not be too close to a
negative integer such that the accuracy of the result is less than half
precision.
Example¶
In this example, \(\psi_1 (1.915)\) is evaluated.
from __future__ import print_function
from numpy import *
from pyimsl.math.psi1 import psi1
x = 1.915
ans = psi1(x)
print("psi1(%f) = %f" % (x, ans))
Output¶
psi1(1.915000) = 0.681164
Warning Errors¶
IMSL_NEAR_NEG_INT_WARN |
The result is accurate to less than
one-half precision because “x ”
is too close to a negative integer. |