For L odd:
For L even:
The triangular window is very similar to a Bartlett window. The Bartlett window always ends with zeros at samples 1 and L, while the triangular window is nonzero at those points. For L odd, the center L-2 points of triang(L-2) are equivalent to bartlett(L).
Create a 200-point triangular window and plot the result using WVTool.
L = 200; wvtool(triang(L))
 Oppenheim, A.V., and R.W. Schafer, Discrete-Time Signal Processing, Prentice-Hall, Englewood Cliffs, NJ, 1989, pp. 447-448.