HP HP-15C - Page 23

Section 1
21
The accuracy of this approximation depends upon the increment A
and the nature of the function. Smaller values of A give better
approximations to the derivative, but excessively small values can
cause round-off inaccuracy. A value of x at which the slope is zero
is potentially a local extreme of the function.
Example: Solve the previous example without using the equation
for the derivative dE/dd.
Find the angle at which the derivative (determined numerically) of
the intensity E is zero.
In Program mode, key in two subroutines: one to estimate the
derivative of the intensity and one to evaluate the intensity
function E. In the following subroutine, the slope is calculated
between 6 + 0.001 and 6 — 0.001 radians (a range equivalent to
approximately 0.1°).
Display
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Program Mode.
Evaluates E at 6 + 0.001.
Evaluates E at 6 - 0.001.