3.2 First plots

The core graph-plotting command of Pyxplot is the plot command. The following simple example plots the trigonometric function $\sin (x)$ :

plot sin(x)

$\includegraphics[width=8cm]{examples/eps/ex_intro_sine}$

This is one of a large number of standard mathematical functions which are built into Pyxplot; a complete alphabetical list of them can be found in Chapter 12.

It is also possible to plot data stored in files. The following would plot data from a file data.dat, taking the $x$ -coordinate of each point from the first column of the data file, and the $y$ -coordinate from the second. The data file is assumed to be in plain text format¹, with columns separated by whitespace and/or commas² :

plot 'data.dat'

Several items can be plotted on the same graph by separating them by commas, as in

plot 'data.dat', sin(x), cos(x)

and it is possible to define one’s own variables and functions, and then plot them, as in the example

a = 0.02
b = -1
c = 5
f(x) = a*(x**3) + b*x + c
plot f(x)

$\includegraphics[width=8cm]{examples/eps/ex_intro_func}$

Pyxplot supports almost all of the same mathematical operators as the C programming language; a complete list of them can be found in Table 3.1. If you have experience of similar tricks in C, it is quite possible to write the following expressions in Pyxplot (but don’t worry if this is a little over your head):

pyxplot> print (a=3)+(b=2)
5
pyxplot> print a0?"yes":"no"
yes
pyxplot> print "%s %s"%(++a,b++)
4 2
pyxplot> print (a+=10 , b+=10 , a+b)
27

In the final example, the comma operator is used as in C, to return only the value of the final comma-separated expression.

Symbol	Description	Operator Associativity
`**`	Algebraic exponentiation	right-to-left
`-`	Unary minus sign	right-to-left
`–`	Unary decrement	right-to-left
`+`	Unary plus sign	right-to-left
`++`	Unary increment	right-to-left
`not !`	Logical not	right-to-left
	Unary one’s complement	right-to-left
`*`	Algebraic multiplication	left-to-right
`/`	Algebraic division	left-to-right
`%`	Modulo operator	left-to-right
`+`	Algebraic sum	left-to-right
`-`	Algebraic subtraction	left-to-right
`<<`	Left binary shift	left-to-right
`>>`	Right binary shift	left-to-right
`<`	Magnitude comparison	right-to-left
`>`	Magnitude comparison	right-to-left
`<=`	Magnitude comparison	right-to-left
`>=`	Magnitude comparison	right-to-left
`== <>`	Equality comparison	right-to-left
`!=`	Equality comparison	right-to-left
`&`	Binary and	left-to-right
	Binary exclusive or	left-to-right
`\|`	Binary or	left-to-right
`and &&`	Logical and	left-to-right
`or \|\|`	Logical or	left-to-right
`?:`	Ternary conditional	right-to-left
`=`	Assignment operator	right-to-left
`+= -= *=`	Assignment operators	right-to-left
`/= %= &=`
`= \|=`
`<<= >>=`
`,`	Comma separator	left-to-right

Table 3.1: A list of mathematical operators which Pyxplot recognises, in order of descending precedence. Items separated by horizontal rules are of differing precedence; those not separated by horizontal rules are of equal precedence. The third column indicates whether strings of operators are evaluated from left to right, or from right to left. For example, the expression x**y**z is evaluated as (x**(y**z)).

Footnotes

If the filename of a data file ends with a .gz suffix, it is assuming to be gzipped plaintext, and is decoded accordingly. Other formats of data file can be opened with the use of input filters; see Section 5.1.
This format is compatible with the Comma Separated Values (CSV) format produced by many applications such as Microsoft Excel.