INTERFACE R2;

(*
  Linear algebra in R^2.
  Created 94-05-04 by J. Stolfi.
  Last edited by stolfi *)

IMPORT Wr;

TYPE T = ARRAY [0..1] OF REAL;

CONST
  N = 2;
  Zero = T{0.0, ..};
  Ones = T{1.0, ..};
  Axis = ARRAY [0..1] OF T{
    T{1.0, 0.0},
    T{0.0, 1.0}
  };

PROCEDURE Add(READONLY a, b: T): T;
  (*
    Returns "a + b". *)

PROCEDURE Sub(READONLY a, b: T): T;
  (*
    Returns "a - b". *)

PROCEDURE Neg(READONLY a: T): T;
  (*
    Returns "-a" *)

PROCEDURE Scale(s: LONGREAL; READONLY a: T): T;
  (*
    Returns "s * a"; *)

PROCEDURE Weigh(READONLY a, b: T): T;
  (*
    Returns "a" times "b" componentwise. *)

PROCEDURE Mix(s: LONGREAL; READONLY a: T; t: LONGREAL; READONLY b: T): T;
  (*
    Returns "s * a + t * b". *)

PROCEDURE Length(READONLY a: T): LONGREAL;
  (*
    Returns the Euclidean norm (length) of vector "a". *)
    
PROCEDURE LInfLength(READONLY a: T): REAL;
  (*
    Returns the L_infinity norm of vector "a", i.e. the max absolute coordinate. *)

PROCEDURE LengthSqr(READONLY a: T): LONGREAL;
  (*
    Returns the square of the Euclidean length of vector "a", i.e. Dot(a,a). *)

PROCEDURE Dist(READONLY a, b: T): LONGREAL;
  (*
    Returns the Euclidean distance between points "a" and "b". *)
    
PROCEDURE DistSqr(READONLY a, b: T): LONGREAL;
  (*
    Returns the square of the Euclidean distance between points "a" and "b". *)
    
PROCEDURE LInfDist(READONLY a, b: T): REAL;
  (*
    Returns the max absolute difference between the coordinates of "a" and "b". *)

PROCEDURE Dir(READONLY a: T): T;
  (*
    Returns the vector "a" scaled to unit Euclidean norm. *)

PROCEDURE LInfDir(READONLY a: T): T;
  (*
    Returns the vector "a" scaled to unit L_infinity norm. *)

PROCEDURE Dot(READONLY a, b: T): LONGREAL;
  (*
    Returns the dot product of vectors "a" and "b". *)

PROCEDURE Det(READONLY a, b: T): LONGREAL;
  (*
    Returns the determinant of the matrix whose rows are "a" and "b". *)

PROCEDURE Cross(READONLY a: T): T;
  (*
    Returns the `cross product' of "a": a vector such that 
    "Dot(Cross(a), b) = Det(a, b)" for all "b".  
    This is just "a" rotated 90 degrees counterclockwise. *)

PROCEDURE Project(READONLY a, u: T): T;
  (*
    Returns the component of vector "a" that is parallel to "u". *)

PROCEDURE Orthize(READONLY a, u: T): T;
  (*
    Returns the component of vector "a" that is orthogonal to "u". *)
    
PROCEDURE Print(wr: Wr.T; READONLY a: T);
  (*
    Prints "a" to the given writer. *)

END R2.