Riemann Sum

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Riemann Sum
Graph the
Riemann sum of
as x goes from to
using rectangles
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Let a closed interval [a,b] be partitioned by points a<x_1<x_2<...<x_(n-1)<b, where the lengths of the resulting intervals between the points are denoted Deltax_1, Deltax_2, ..., Deltax_n. Let x_k^* be an arbitrary point in the kth subinterval. Then the quantity

 sum_(k=1)^nf(x_k^*)Deltax_k

is called a Riemann sum for a given function f(x) and partition, and the value maxDeltax_k is called the mesh size of the partition.

If the limit of the Riemann sums exists as maxDeltax_k->0, this limit is known as the Riemann integral of f(x) over the interval [a,b]. The shaded areas in the above plots show the lower and upper sums for a constant mesh size.

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