calc: Basic Graphics
14.1 Basic Graphics
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The easiest graphics command is ‘g f’ (‘calc-graph-fast’). This command
takes two vectors of equal length from the stack. The vector at the top
of the stack represents the “y” values of the various data points. The
vector in the second-to-top position represents the corresponding “x”
values. This command runs GNUPLOT (if it has not already been started
by previous graphing commands) and displays the set of data points. The
points will be connected by lines, and there will also be some kind of
symbol to indicate the points themselves.
The “x” entry may instead be an interval form, in which case suitable
“x” values are interpolated between the minimum and maximum values of
the interval (whether the interval is open or closed is ignored).
The “x” entry may also be a number, in which case Calc uses the
sequence of “x” values ‘x’, ‘x+1’, ‘x+2’, etc. (Generally the number 0
or 1 would be used for ‘x’ in this case.)
The “y” entry may be any formula instead of a vector. Calc
effectively uses ‘N’ (‘calc-eval-num’) to evaluate variables in the
formula; the result of this must be a formula in a single (unassigned)
variable. The formula is plotted with this variable taking on the
various “x” values. Graphs of formulas by default use lines without
symbols at the computed data points. Note that if neither “x” nor “y”
is a vector, Calc guesses at a reasonable number of data points to use.
See the ‘g N’ command below. (The “x” values must be either a vector or
an interval if “y” is a formula.)
If “y” is (or evaluates to) a formula of the form ‘xy(X, Y)’ then the
result is a parametric plot. The two arguments of the fictitious ‘xy’
function are used as the “x” and “y” coordinates of the curve,
respectively. In this case the “x” vector or interval you specified is
not directly visible in the graph. For example, if “x” is the interval
‘[0..360]’ and “y” is the formula ‘xy(sin(t), cos(t))’, the resulting
graph will be a circle.
Also, “x” and “y” may each be variable names, in which case Calc
looks for suitable vectors, intervals, or formulas stored in those
variables.
The “x” and “y” values for the data points (as pulled from the
vectors, calculated from the formulas, or interpolated from the
intervals) should be real numbers (integers, fractions, or floats). One
exception to this is that the “y” entry can consist of a vector of
numbers combined with error forms, in which case the points will be
plotted with the appropriate error bars. Other than this, if either the
“x” value or the “y” value of a given data point is not a real number,
that data point will be omitted from the graph. The points on either
side of the invalid point will _not_ be connected by a line.
See the documentation for ‘g a’ below for a description of the way
numeric prefix arguments affect ‘g f’.
If you store an empty vector in the variable ‘PlotRejects’ (i.e., ‘[
] s t PlotRejects’), Calc will append information to this vector for
every data point which was rejected because its “x” or “y” values were
not real numbers. The result will be a matrix where each row holds the
curve number, data point number, “x” value, and “y” value for a rejected
data point. 
Evaluates-To Operator, for a handy way to keep tabs
on the current value of ‘PlotRejects’. Operations on Variables,
for the ‘s R’ command which is another easy way to examine
‘PlotRejects’.
To clear the graphics display, type ‘g c’ (‘calc-graph-clear’). If
the GNUPLOT output device is an X window, the window will go away.
Effects on other kinds of output devices will vary. You don’t need to
use ‘g c’ if you don’t want to—if you give another ‘g f’ or ‘g p’
command later on, it will reuse the existing graphics window if there is
one.
Info Catalog
calc: Graphics
calc: Graphics
calc: Three Dimensional Graphics