HP 40gs User Manual page 250

Psi
REORDER
SEVAL
SIGMA
14-68
gives:
5 1
2
-- - π ⋅
-- -
– +
4 6
Returns the value of the Digamma function at a.
The Digamma function is defined as the derivative of
ln(Γ(x)), so we have PSI(a,0) = Psi(a).
Example
Typing:
Psi(3)
and pressing
gives:
.922784335098
Reorders the input expression following the order of
variables given in the second argument.
Example
Typing:
2
REORDER(X + 2 · X · A + A
AND Z)
gives:
2
⋅ ⋅
A + 2 X A +
SEVAL simplifies the given expression, operating on all
but the top-level operator of the expression.
Example
Typing:
SEVAL(SIN(3 · X -– X) + SIN(X + X))
gives:
( 2 x ⋅ )
sin + sin
Returns the discrete antiderivative of the input function,
that is, the function G, that satisfies the relation G(x + 1)
– G(x) = f(x). It has two arguments: the first is a function
f(x) of a variable x given as the second argument.
2
+ Z
2 2
⋅
X – Z X + Z
( 2 x ⋅ )
Computer Algebra System (CAS)
2
– X · Z, A AND X