Triangle Function

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The triangle function is the function

Lambda(x)={0 |x|>=1; 1-|x| |x|<1
(1)
=Pi(x)*Pi(x)
(2)
=Pi(x)*H(x+1/2)-Pi(x)*H(x-1/2),
(3)

where Pi(x) is the rectangle function, H(x) is the Heaviside step function, and * denotes convolution. An obvious generalization used as an apodization function goes by the name of the Bartlett function.

The piecewise version of the triangle function is implemented in the Wolfram Language as UnitTriangle[x], while the generalized function version is implemented as HeavisideLambda[x].

TriangleFunction3D

There is also a three-argument function known as the triangle function,

 lambda(x,y,z)=x^2+y^2+z^2-2xy-2xz-2yz.
(4)

It follows that

 lambda(a^2,b^2,c^2)=(a+b+c)(a+b-c)(a-b+c)(a-b-c).
(5)

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