HP HP-28S - Page 40

HP-28S
the plot axes. Set by AXES.
See Reserved Variables.
STEQ Store a function in variable EQ. The form of the function determines
how it is displayed:
• An expression is displayed as a single curve.
• An equation results in two curves, one for each side of the equal-
sign.
• A program is treated as expression and plots a single curve. The
program must not take any arguments from the stack and it must
returns a single function result to the stack.
See Reserved Variables.
RCEQ Recall the function from EQ.
PMIN Takes a complex argument from the stack and stores it in PPAR as the
lower left corner of the plot.
PMAX Takes a complex argument from the stack and stores it in PPAR as the
upper right corner of the plot.
INDEP Store a name in PPAR which specifies the independent variable for a
plot. The function stored in EQ is evaluated for varying values of the
independent variable in order to obtain the y=f(x) values of the curve to
be plotted.
If no independent variable has been specified then DRAW uses the first
variable in EQ instead.
DRAW When called by pressing the DRAW menu button:
• Clears the display
• Calls DRAX to draw the axes and then draws the plot.
• Dependent on the type of the function either one or two curves are
plotted, see STEQ above.
• Interactive mode is activated, see below.
• Pressing ON aborts the plot process and interactive mode activated
immediately.
When called from a program:
• The display is not cleared.
• Axes are not drawn.
• The 1 or 2 function curves are plotted.
• Pressing ON aborts the plot process and returns to the stack view.
• Pressing any key after the plot has been drawn returns to the stack
view.
• Interactive mode is not entered automatically but can be invoked
using the DIGTZ command.
This non-interactive mode allows to overlay multiple function plots:
<< 'PPAR' PURGE (0,0) PMIN (10 4) PMAX
'X' INDEP CLLCD DRAX
'SIN(X)+1' STEQ DRAW
'(COS(X*1,5)+1)*1.5' STEQ DRAW
'(X-5)^2/10 + 0.5' STEQ DRAW
DIGTZ >>
Draws an overlay of three plots and then activates interactive mode.
Interactive
Mode
While the plot is displayed:
• The cursor keys can be used to move a small cross-hair-shaped ("+")
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