| Example: Let for . Then, for . Further, for . The length of the curve joining and is . Definition (Smooth Curve or Regular Curve): A curve ( ) is said to be a smooth curve or regular curve if (i) the derivative exist and continuous for and (ii) for .
Examples: The circle for , the straight line segment for and the curve for are smooth curves. Definition (Contour or Piecewise Smooth Curve): A contour or piecewise smooth curve , is a curve consisting of a finite number of smooth curves joined end to end
Examples: Any oriented polygonal path, circular path are contours.
Definition (Simple Closed Contour): A contour ( ) having only the initial and final values are same is called a simple closed contour .
Examples: Any oriented triangle or rectangle or circle are examples of simple closed contours.
Definition (Opposite Curve): Consider the curve having parametrization for . The opposite curve , denoted by , traces out the same set of points in the complex plane but in the reverse order, and it has the parametrization |