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Can it be concluded generally that:

[tex]

\sum_r dx_r = 0

[/tex]

...because we are summing an infinitesimaly small variable a finite number of times, in contrast to an integral which is an infinite sum of infinitesimaly small variables? In one of my books a probability is given by:

[tex]

p_r = \frac{1}{Z} Exp[-\beta E_r]

[/tex]

... and in the next line they write that:

[tex]

\sum_r dp_r = 0

[/tex]

Does someone have an explanation to this?

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# Sum of an infinitesimal variable

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