13.11.1  Circles and arcs in the plane: circle

See also Section 13.11.2.

See Section 14.10 for circles in space.

The circle command creates circles and arcs. You can specify the circle in different ways.

• • circle can take one argument:
    eqn, the equation of a circle with variables x and y (or an expression assumed to be set to 0).
    
  • circle(eqn) returns and draws the circle.

  
  

  Example.
  Input:

  circle(x2 + y2 - 2*x - 2*y)

  Output:

  
• • circle can take two arguments:
    • P, a point.
    • α, a complex number.
  • circle(P,α) returns and draws the circle centered at P and whose radius is |α|.

  
  

  Example.
  Input:

  circle(-1,i)

  Output:

  
• • circle can take two arguments:
    A,B, two points (where B must be the value of point and not simply the affix).
  • circle(A,B) returns and draws the circle whose diameter is AB.

  
  

  Example.
  Input:

  circle(-1,point(i))

  Output:

  
• • circle can take four mandatory arguments and two optional arguments:
    • C, a point.
    • r, a complex number.
    • a,b, two real numbers.
    • Optionally, var₁,var₂, variable names.
  • circle(C,r,a,b) returns and draws an arc of the circle with center C and radius |r|, with central angles a and b. The angles start on the axis defined by C and C+r.
    If the arguments var₁ and var₂ are given, they will be assigned to the ends of the arc.

  
  

  Examples.

  • Input:
    circle(-1,1,0,pi/4)
    Output:
    
  • Input:
    circle(-1,point(i),0,pi/4)
    Output: