Purpose

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  This function uses the trapezoidal rule to perform a running
  integration of tabulated data. It is adapted from the tsum routine
  in the IDL astronomy user's library, but returns the integral at
  each point of x, and not just over one large region.

Category

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  Numerical recipes

Inputs

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  x: Input x values
  y: Input y values

Outputs

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  Integral(y dx) from x[0] to x[i]. A vector of the same length as x
  and y.

Modification History

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  September 2009: Lifted from IDL astronomy user's library by Chris Beaumont