cross_product

EXPRESS specification:

FUNCTION cross_product
(* Modified for LPM/6 *)(arg1, arg2 : direction) : vector; LOCAL mag : REAL; res : direction; v1,v2 : LIST[3:3] OF REAL; result : vector; END_LOCAL; IF ( NOT EXISTS (arg1) OR (arg1.dim = 2)) OR ( NOT EXISTS (arg2) OR (arg2.dim = 2)) THEN RETURN(?); ELSE BEGIN v1 := normalise(arg1).direction_ratios; v2 := normalise(arg2).direction_ratios; res := dummy_gri || direction([(v1[2]*v2[3] - v1[3]*v2[2]), (v1[3]*v2[1] - v1[1]*v2[3]), (v1[1]*v2[2] - v1[2]*v2[1])]); mag := 0.0; REPEAT i := 1 TO 3; mag := mag + res.direction_ratios[i]*res.direction_ratios[i]; END_REPEAT; IF (mag > 0.0) THEN result := dummy_gri || vector(res, SQRT(mag)); ELSE result := dummy_gri || vector(arg1, 0.0); END_IF; RETURN(result); END; END_IF;
END_FUNCTION;