The left graph below is the domain coloring graph of $w=f(z)$. Here, at the point $z$, the hue and brightness are $\arg(w)$ and $|w|$ respectively (red is $\arg(w)=0$, black is $|w|=0$, white is $|w|=\infty$).
The right graph, provided for reference, is the baseline color graph, corresponding to $w=z$. For a sense of scale, the unit circle is drawn. Enter the complex function $f(z)$ in the text box then hit < tab > to graph it. For complex number syntax, see below.
Enter monomials, polynomials, rational functions, $e^z$, etc. The graph bounding box dimension is $2b\times 2b$. By adjusting $b$, zoom in to and out of poles and zeros located at the origin.
SageMath code below is in blue boxes.
Lowercase, uppercase, camelcase.
show(...) displays the result, whether it is a number, an equation, a graph, a surface, etc.
Addition a + b, subtraction a - b, multiplication a * b, division a / b, mod a % b, powers a ^ b, and parentheses (...). For example,
show(5 + 14) show(15 * 10) show(23 % 5) show(46 / 10)outputs \(19\) and \(150\) and \(3\) and \(23/5\).
To convert a number a to a decimal with n digits, write N(a,digits=n). For example, the code
a = 1234/1728 show(a) a = N(a,digits=20) show(a)outputs \(617/864\) and \(0.71412037037037037037\).
The code
a = sqrt(25) b = sqrt(1234/1728) c = N(b,digits=40) show(a) show(b) show(c)outputs \(5\) and \(\dfrac1{12}\sqrt{\dfrac{617}6}\) and \(0.8450564302875698314535479970302979455774\).
Equal a == b, not equal a != b, less than a < b, greater than a > b, less or equal a <= b, greater or equal a >= b. The code
show(5^2 == 25) show(15 != 10) show(15 <= 10)outputs "True" and "True" and "False".
if <conditional>: is a header announcing the start of an if block of code. The code block after the header is executed if the conditional is True. The code block after the header is always indented:
if d^2 > 9: ... first line of code block ... second line of code block
[a,b,c,...] (enclosed in brackets).
range(5)
is the same as 0,1,2,3,4 and range(2,9) is the same as 2,3,4,5,6,7,8.
for i in range(5): and for i in range(2,9): are headers announcing the start of a for block. The code block after the header is executed repeatedly with the index i taking sequentially the values in the range.
The code block after the header is always indented:
for i in range(2,9): ... first line of code block ... second line of code block
This is how SageMath stores the data in a drawing of a point, a line, a graph, a surface, etc. It is stored in the computer as a graphics object. Graphics objects A, B, C, etc. may be combined by writing
A + B + C + etc. Graphics objects are displayed using show.
f(x) = x^2*sin(x) or g(x,y)= x^2*sin(x*y) are functions. Evaluate functions using a = f(x=2) or b = g(x=3). Then show(a) results in \(4\sin2\) and show(b) results in \(9\sin(3y)\).
Sometimes x is a constant, sometimes x is a variable. The code
x = 2 show(x)outputs \(2\). Here
x is a constant. The value of the constant x is \(2\).
The code
var('x')
show(x)
outputs \(x\). Here x is a variable. The code var('x','y','a') defines three variables x, y, a. Defining a function f(x) = x^2 automatically makes x a variable.
The code
f(x) = x^2
m = 2
b = 4
var('y')
show(y == m*x+b)
show(y == f(x))
outputs the equations \(y=2x+4\) and \(y=x^2\). Equations can be given names, for example
var('x','y')
eq = y == 2*x+4
show(eq)
outputs \(y=2x+4\).
P = point((x,y)) creates a graphics point P corresponding to the point \((x,y)\). To draw it, use show(P).
For multiple points, use points(L) where L is a list of points.
G = plot(f(x),(x,a,b)) creates a graphics plot G corresponding to the plot of the function \(f(x)\) over the interval \(a\le x\le b\).
To draw it, use show(G).
G = polar_plot(f(theta),(theta,a,b)) creates a graphics plot G corresponding to the plot of the function \(f(\theta)\) over the interval \(a\le \theta\le b\).
To draw it, use show(G).
G = plot3d(f(x,y),(x,a,b),(y,c,d)) creates a graphics plot G corresponding to the plot of the function \(f(x,y)\) over the region \(a\le x\le b\), \(c \le y \le d\).
To draw it, use show(G).
Complex numbers are written as usual x+y*i or r*e^(i*theta). The code abs(z), arg(z) yield the absolute value, argument of $z$, conjugate(z) is the conjugate of $z$, and z.real(), z.imag() are the real and imaginary parts of $z$.
The code complex_plot(f, (a,b),(c,d)) draws the complex function \(f(z)\) over the region \(a\le x\le b\), \(c\le y\le d\).
Here the brightness is $r$ ($r=0$ is black) and the hue is $\theta$ ($\theta=0$ is red), where $f(z)=re^{i\theta}$.
To plot multiple functions \(f,g,h\) at the same time, enter them into plot or plot3d etc. as a list [f,g,h].
line([(x_1,y_1),(x_2,y_2)]) creates a graphics line segment corresponding to the line segment joining the points \((x_1,y_1)\) and \((x_2,y_2)\). Notice the two points are inside a list [...]. Can have more than two points, for example, if L=[a,b,c,d] is a list of four points, then show(line(L)) draws the line segments joining the points \(a\), \(b\), \(c\), \(d\) in order.
Write derivative(f,x) or Df(x) = derivative(f,x).
To show it, write show(derivative(f,x)) or show(Df(x)).
A string is any sequence of characters enclosed in quotes '...', for example 'alpharomeo'. The string '2' is different than the number 2.
You can add color to a plot by writing plot(f,x,a,b,color='blue').
You can add a label 'alpharomeo' to a plot by writing plot(f,x,a,b,legend_label='alpharomeo').